Network Architecture, Methods, and Devices for a Wireless Communications Network

ABSTRACT

Methods and apparatus in a fifth-generation wireless communications, including an example method, in a wireless device, that includes receiving a downlink signal comprising an uplink access configuration index, using the uplink access configuration index to identify an uplink access configuration from among a predetermined plurality of uplink access configurations, and transmitting to the wireless communications network according to the identified uplink access configuration. The example method further includes, in the same wireless device, receiving, in a first subframe, a first Orthogonal Frequency-Division Multiplexing (OFDM) transmission formatted according to a first numerology and receiving, in a second subframe, a second OFDM transmission formatted according to a second numerology, the second numerology differing from the first numerology. Variants of this method, corresponding apparatuses, and corresponding network-side methods and apparatuses are also disclosed.

TECHNICAL FIELD

The present disclosure is related to wireless communications networksand describes network architecture, wireless devices, and wirelessnetwork nodes suitable for, but not limited to, a fifth-generation (5G)wireless communications network.

BACKGROUND

There are three main challenges that need to be addressed by a so-called5G wireless communication system to enable a truly “networked society,”where information can be accessed and data shared anywhere and anytime,by anyone and anything. These are:

-   -   A massive growth in the number of connected devices.    -   A massive growth in traffic volume.    -   An increasingly wide range of applications with varying        requirements and characteristics.

To handle massive growth in traffic volume, wider frequency bands, newspectrum, and in some scenarios denser deployment are needed. Most ofthe traffic growth is expected to be indoor and thus indoor coverage isimportant.

New spectrum for 5G is expected to be available after 2020. The actualfrequency bands, and the amount of spectrum, have not yet beenidentified. The identification of frequency bands above 6 GHz for mobiletelecommunications will be handled in the World Radio Conference in 2019(WRC-19). New frequency bands below 6 GHz for mobile telecommunicationsare handled in WRC-15. Eventually, all mobile telecommunications bands,from below 1 GHz, up to as high as 100 GHz, could potentially becomecandidates for 5G. However, it is expected that the first commercialdeployment of 5G will happen in frequency bands close to 4 GHz, and that28 GHz deployments will come later.

The International Telecommunication Union (ITU) has outlined a visionfor 5G, which it will refer to as “IMT-2020,” providing a first glimpseof potential scenarios, use cases and related ITU requirements thateventually will define 5G.

The 3rd-generation Partnership Project (3GPP) has begun its journeytowards 5G, with a 5G workshop held in September 2015. A study item onchannel modelling for spectrum above 6 GHz has been approved.Development of specifications for 5G in 3GPP is likely to be splitacross multiple releases, with two phases of normative work. Phase 1 isexpected to be completed in the second half of 2018. It will fulfil asubset of the complete set of requirements and target the need for earlycommercial deployments in 2020 expressed by some operators. Phase 2,targeted for completion by the end of 2019, will meet all identifiedrequirements and use cases.

SUMMARY

Embodiments of the various techniques, devices, and systems disclosedherein include wireless devices and methods carried out by such devices.An example of such a method includes receiving a downlink signalcomprising an uplink access configuration index, using the uplink accessconfiguration index to identify an uplink access configuration fromamong a predetermined plurality of uplink access configurations, andtransmitting to the wireless communications network according to theidentified uplink access configuration. The method also includesreceiving, in a first subframe, a first OFDM transmission formattedaccording to a first numerology and receiving, in a second subframe, asecond OFDM transmission formatted according to a second numerology, thesecond numerology differing from the first numerology. The first OFDMtransmission may have a numerology according to the 3GPP specificationsfor LTE, for example.

The first and second numerologies may comprise subframes of first andsecond subframe lengths, respectively, where the first subframe lengthdiffers from the second subframe length. The first numerology may alsohave a first subcarrier spacing and the second numerology may have asecond subcarrier spacing, where the first subcarrier spacing differsfrom the second subcarrier spacing.

The method may further include receiving and processing first Layer 2data on a first physical data channel and receiving and processingsecond Layer 2 data on a second physical data channel. The receiving andprocessing of the first Layer 2 data comprises the use of soft HARQcombining, and the receiving and processing of the second Layer 2 datacomprises no soft HARQ combining. This may include using a common set ofdemodulation reference signals for receiving both the first and secondLayer 2 data.

In some cases, a single RRC approach may be used. For example, themethod in a wireless device may further include processing data from thefirst OFDM transmission using a first MAC protocol layer and processingdata from the second OFDM transmission using a second MAC protocollayer, where the first MAC protocol layer differs from the second MACprotocol layer. The method may further include processing messagesreceived from each of the first and second MAC protocol layers using asingle, common RRC protocol layer.

In some cases, a dual RRC approach may be used. In this case, the methodin the wireless device further includes processing data from the firstOFDM transmission using a first MAC protocol layer and processing datafrom the second OFDM transmission using a second MAC protocol layer,where the first MAC protocol layer differs from the second MAC protocollayer. The method may further include processing messages received viathe first MAC protocol layer using a first RRC protocol layer andprocessing messages received via the second MAC protocol layer using asecond RRC protocol layer, where the first RRC protocol layer differsfrom the second RRC protocol layer. At least a first one of the firstand second RRC protocol layers is configured to pass selected RRCmessages to the other one of the first and second RRC protocol layers.The selected RRC messages are RRC messages received and processed by thefirst one of the first and second RRC protocol layers but targeted forthe other one of the first and second RRC protocol layers.

The method in the wireless device may further include transmitting thirdLayer 2 data on a third physical data channel and transmitting fourthLayer 2 data on a fourth physical data channel. The transmitting of thethird Layer 2 data comprises the use of a HARQ process supporting softcombining, and the transmitting of the fourth Layer 2 data comprises noHARQ process.

In some cases, the method includes operating in a connected mode for oneor more first intervals and operating in a dormant mode for one or moresecond intervals, where the first and second OFDM transmissions areperformed in the connected mode. Operating in the dormant mode comprisesmonitoring signals carrying tracking area identifiers, comparingtracking area identifiers received during the monitoring with a trackingarea identifier list, and notifying the wireless communication networkin response to determining that a received tracking area identifier isnot on the list but otherwise refraining from notifying the wirelesscommunication network in response to receiving changing tracking areaidentifiers.

The method in the wireless device may include transmitting, to thewireless communications network, a capability pointer, the capabilitypointer identifying a set of capabilities, for the wireless device,stored in the wireless communications network. The method may includetransmitting to the wireless communications network using acontention-based access protocol. The contention-based access protocolmay comprise a listen-before-talk (LBT) access mechanism.

The method in the wireless device may further include measuring a firstmobility reference signal on a first received beam and measuring asecond mobility reference signal on a second received beam, where thesecond mobility reference signal differs from the first mobilityreference signal. The method may further include reporting results ofmeasuring the first and second mobility reference signals to thewireless communications network. The method may also include receiving,in response to reporting the results, a command to switch from receivingdata on a current downlink beam to receiving data on a differentdownlink beam. The method may include receiving a timing advance valuefor application to the different downlink beam.

Other embodiments of the various techniques, devices, and systemsdisclosed herein include radio network equipment and methods carried outby one or more instances of such radio network equipment. An example ofsuch a method includes transmitting a first downlink signal comprisingan uplink access configuration index, the uplink access configurationindex identifying an uplink access configuration from among a pluralityof predetermined uplink access configurations, and subsequentlyreceiving a transmission from a first wireless device according to theidentified uplink access configuration. The method also includestransmitting, in a first subframe, a first OFDM transmission formattedaccording to a first numerology and transmitting, in a second subframe,a second OFDM transmission formatted according to a second numerology,the second numerology differing from the first numerology.

In some cases, the transmitting of the first downlink signal isperformed by a first instance of radio network equipment, while thetransmitting of the first and second OFDM transmissions is performed bya second instance of radio network equipment. The first OFDMtransmission may have a numerology according to the specifications forLTE, for example.

The first and second numerologies may comprise subframes of first andsecond subframe lengths, respectively, where the first subframe lengthdiffers from the second subframe length. The first numerology may have afirst subcarrier spacing and the second numerology may have a secondsubcarrier spacing, where the first subcarrier spacing differs from thesecond subcarrier spacing.

The method carried out by radio network equipment may includetransmitting a second downlink signal comprising an access informationsignal, the access information signal indicating a plurality of uplinkaccess configurations, where the uplink access configuration indexidentifies one of the plurality of uplink access configurations. Thetransmitting of the second downlink signal may be performed by a thirdinstance of radio network equipment.

In some cases, the method in the radio network equipment includesprocessing and transmitting first Layer 2 data on a first physical datachannel and processing and transmitting second Layer 2 data on a secondphysical data channel. The processing and transmitting of the firstLayer 2 data comprises the use of a HARQ process supporting softcombining, and the processing and transmitting of the second Layer 2data comprises no HARQ process. The transmitting of the first and secondLayer 2 data may be performed using a common antenna port, where themethod further includes transmitting a common set of demodulationreferences, using the common antenna port, for use in receiving both thefirst and second Layer 2.

The method in the radio network equipment may include receiving andprocessing third Layer 2 data on a third physical data channel andreceiving and processing fourth Layer 2 data on a fourth physical datachannel, where the receiving and processing of the third Layer 2 datacomprises the use of soft HARQ combining and the receiving andprocessing of the fourth Layer 2 data comprises no soft HARQ combining.

In some cases, the transmitting of the first and second OFDMtransmissions may be performed by one instance of the radio networkequipment, where the method further includes processing data for thefirst OFDM transmission using a first MAC protocol layer and processingdata for the second OFDM transmission using a second MAC protocol layer,the first MAC protocol layer differing from the second MAC protocollayer. The method may further include processing messages to betransported by each of the first and second MAC protocol layers, using asingle, common RRC protocol layer.

In other cases, the transmitting of the first and second OFDMtransmissions is performed by one instance of the radio networkequipment, where the method further includes processing data for thefirst OFDM transmission using a first MAC protocol layer and processingdata, for the second OFDM transmission using a second MAC protocollayer, the first MAC protocol layer differing from the second MACprotocol layer. The method in some embodiments further includesprocessing messages to be transported by the first MAC protocol layer,using a first RRC protocol layer, and processing messages to betransported by the second MAC protocol layer, using a second RRCprotocol layer, where the first RRC protocol layer differs from thesecond RRC protocol layer. At least a first one of the first and secondRRC protocol layers is configured to pass selected RRC messages to theother one of the first and second RRC protocol layers, the selected RRCmessages being RRC messages received and processed by the first one ofthe first and second RRC protocol layers but targeted for the other oneof the first and second RRC protocol layers.

The method in the radio network equipment may further include receiving,from a second wireless device, a capability pointer, the capabilitypointer identifying a set of capabilities for the second wirelessdevice, and retrieving the set of capabilities for the second wirelessdevice, from a database of stored capabilities for a plurality ofwireless devices, using the received capability pointer.

The method in the radio network equipment may include transmitting to athird wireless device, using a contention-based protocol. Thecontention-based access protocol may comprise an LBT access mechanism.

In some embodiments, the method in the radio network equipment includesreceiving a random access request message from a fourth wireless device,via an uplink beam formed using multiple antennas at the radio networkequipment, estimating an angle-of-arrival corresponding to the randomaccess request message and transmitting a random access responsemessage, using a downlink beam formed using multiple antennas at theradio network equipment. Forming the downlink beam is based on theestimated angle-of-arrival. The uplink beam may be a swept uplink beam.A width of the downlink beam may be based on an estimated quality of theestimated angle-of-arrival.

The method in the radio network equipment may include serving a fifthwireless device, where serving the fifth wireless device comprisessending data from the fifth wireless device to a first network node orfirst set of network nodes, according to a first network sliceidentifier associated with the fifth wireless device. The method mayalso include serving a sixth wireless device, where serving the sixthwireless device comprises sending data from the sixth wireless device toa second network node or second set of network nodes, according to asecond network slice identifier associated with the sixth wirelessdevice. The second network slice identifier differs from the firstnetwork slice identifier, and the second network node or second set ofnetwork nodes differs from the first network node or first set ofnetwork nodes.

Other embodiments detailed herein include wireless devices, radionetwork equipment, and systems configured to carry out one or more ofthe methods summarized above and/or one or more of the numerous othertechniques, procedures, and methods described herein, as well ascomputer program products and computer-readable media embodying one ormore of these methods, techniques, and procedures.

Certain embodiments of the present disclosure may provide one or moretechnical advantages. For example, some embodiments may provide supportfor higher frequency bands, compared to conventional wireless systems,with wider carrier bandwidth and higher peak rates, e.g., using newnumerologies, as detailed below. Some embodiments may provide supportfor lower latencies, through the use of shorter and more flexibleTransmission Time Intervals (TTIs), new channel structures, etc. Someembodiments may provide support for very dense deployments, energyefficient deployments and heavy use of beam forming, enabled by, forexample, removing legacy limitations in relation to CRS, PDCCH, etc.Finally, some embodiments provide support for new use cases, servicesand customers such as MTC scenarios including V2X, etc., e.g., throughmore flexible spectrum usage, support for very low latency, higher peakrates etc. Various combinations of the techniques described herein mayprovide these and/or other advantages in a complementary and synergisticway to achieve all or some of the ITU-2020 requirements. Otheradvantages may be readily available to one having skill in the art.Certain embodiments may have none, some, or all of the recitedadvantages.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a high-level logical architecture for NX and LTE.

FIG. 2 shows an NX and LTE logical architecture.

FIG. 3 illustrates LTE/NX UE states.

FIG. 4 is a plot showing an estimate of UE battery life for a UE indormant state, when the network is synchronized, for each of several SSIperiods and DRX cycles.

FIG. 5 a plot showing an estimate of UE battery life for a UE in dormantstate, when the network is not synchronized, for each of several SSIperiods and DRX cycles.

FIG. 6 shows a protocol architecture for a single-RRC protocol track,for LTE-NX dual connectivity.

FIG. 7 shows a protocol architecture for a dual-RRC protocol track, forLTE-NX dual connectivity.

FIG. 8 is an overall RRC signaling diagram for LTE-NX dual connectionsetup.

FIG. 9 illustrates a common (shared) security setup for LTE and NX.

FIG. 10 illustrates an example of UE capability handling.

FIG. 11 is a signaling flow diagram illustrating LTE-NX dualconnectivity setup for a single-RRC protocol architecture.

FIG. 12 is a signaling flow diagram illustrating LTE-NX dualconnectivity setup for a dual-RRC protocol architecture.

FIG. 13 is a signaling flow diagram illustrating a RRC connectionre-activation procedure.

FIG. 14 is a signaling flow diagram illustrating UE-initiated LTE-NXdual connectivity establishment.

FIG. 15 illustrates an example scheduler decision for scheduling aninformation element on a low-delay “direct” channel or anefficiency-optimized “re-transmittable” channel.

FIG. 16 shows use of the PDCCH to enable high-gain beam-forming andin-beam transmission of control information.

FIG. 17 shows various uses of the PDCCH.

FIG. 18 illustrates an example of possible error propagation scenarioswhen using in-band DCI to update a UE search space.

FIG. 19 shows the reporting back of reception success of the dPDCH, by aUE.

FIG. 20 illustrates the use of a single set of terminal-specificdemodulation reference signals for demodulation of two physicalchannels.

FIG. 21 illustrates a basic MAC channel structure for NX.

FIG. 22 shows a transport channel structure and MAC-header format.

FIG. 23 shows an example of how LCID tables may be extended.

FIG. 24 illustrates an example downlink channel structure.

FIG. 25 illustrates an example uplink channel structure.

FIG. 26 shows an example of group scheduling.

FIG. 27 illustrates an ADSS pattern and dimension of DSSI for ADSS.

FIG. 28 illustrates scheduled-based access versus contention-basedaccess.

FIG. 29 shows prioritization between scheduled data and contention-baseddata access.

FIG. 30 illustrates contention-based access with collision avoidanceutilizing LBT and CTS.

FIG. 31 shows an example of a proactive RTS/CTS scheme with selectiveRTS.

FIG. 32 illustrates an improved ARQ for single-hop NX, including“super-fast” feedback and “scheduled” feedback.

FIG. 33 shows an example where fast HARQ feedback is transmitted at theend of the first available UL transmission occasion.

FIG. 34 shows the transmitting of polled HARQ feedback reports.

FIG. 35 illustrates that the number of HARQ processes for which the UEperforms soft packet combining may depend on the packet size.

FIG. 36 illustrates three possible multi-hop/self-backhauled ARQarchitectures.

FIG. 37 shows a multi-hop relay ARQ protocol architecture.

FIG. 38 shows an overview of a multi-hop architecture to support relayrouting.

FIG. 39 illustrates an example of dynamic scheduling.

FIG. 40 shows contention resolution for contention-based instant uplinkaccess.

FIG. 41 illustrates group polling using contention-free andcontention-based access.

FIG. 42 shows an example of MU-MIMO scheduling.

FIG. 43 shows another example of MU-MIMO scheduling

FIG. 44 shows an example of downlink data transmission using reciprocalmassive MIMO beamforming.

FIG. 45 shows an example of uplink data transmission using reciprocalmassive MIMO beamforming

FIG. 46 includes a block diagram of filtered/windowed OFDM processingand shows mapping of subcarriers to time-frequency plane.

FIG. 47 shows windowing of an OFDM symbol.

FIG. 48 illustrates basic subframe types.

FIG. 49 illustrates frame structures for TDD.

FIG. 50 shows an example transmission of an uplink grant.

FIG. 51 shows an example of data and control multiplexing for downlink,in 67.5 kHz numerology.

FIG. 52 shows an example of mapping control and data to physicalresources.

FIG. 53 illustrates example numerologies.

FIG. 54 shows AIT mapping to physical channels.

FIG. 55 provides an overview of PACH transmit processing.

FIG. 56 shows an example of PACH resource mapping.

FIG. 57 illustrates examples of minimum PDCCH allocation units.

FIG. 58 is a graphical representation of LDPC and SC-LDPC codes.

FIG. 59 shows the recursive encoding structure of polar codes.

FIG. 60 shows parallel-concatenated polar encoding for K=2transmissions.

FIG. 61 shows a parallel-concatenated polar decoder, for K=2transmissions.

FIG. 62 illustrates construction of a mobility and access referencesignal (MRS).

FIGS. 63A and 63B show CSI-RS groups, sub-groups, and exampleconfigurations.

FIG. 64 illustrates a preamble format and detector with long coherentaccumulation.

FIG. 65 illustrates USS in relation to MRS and uplink grant includingtiming advance.

FIG. 66 illustrates comb schemes and a RRS design example.

FIG. 67 provides a schematic view of DRMS on a small-scale perspective.

FIGS. 68A and 68B provide a schematic view of DRMS on a large-scaleperspective.

FIG. 69 illustrates uplink latency with SR-SG-data cycle, for FDD mode.

FIG. 70 illustrates latency for TDD.

FIG. 71 shows switching overhead.

FIG. 72 shows an example where fast HARQ feedback is transmitted at theend of a first available uplink transmission occasion.

FIG. 73 shows duplicated end-to-end paths.

FIG. 74 shows uplink radio-access network latency for dynamicscheduling.

FIG. 75 illustrates achievable uplink latency with instant uplinkaccess.

FIG. 76 shows LTE empty sub-frames for several scenarios and LTE energyconsumption for the scenarios.

FIG. 77 shows access information distribution.

FIG. 78 shows access information table (AIT) and system signature index(SSI) transmissions.

FIG. 79 shows AIT transmission methods.

FIG. 80 shows initial random access procedures for UEs with or withoutAIT.

FIG. 81 is a process flow diagram illustrating UE behaviors beforeinitial random access.

FIG. 82 shows duty cycle of AIT/SSI of varying sizes, using 1.4 MHzbandwidth.

FIG. 83 shows AIT and SSI deployment options.

FIG. 84 shows tracking area configuration.

FIG. 85 is a signal flow diagram illustrating a TRA update procedure.

FIG. 86 is a signal flow diagram illustrating an initial attach over NX.

FIG. 87 illustrates random access preamble transmission.

FIG. 88 shows random access response transmission.

FIG. 89 illustrates the realization of different services in differentlogical network slices.

FIG. 90 illustrates examples of network slicing.

FIG. 91 shows a diversity of services with typical resource usage.

FIG. 92 illustrates a simplification of resource allocation for a givenservice or UE.

FIG. 93 shows an example of MAC resource partitioning.

FIG. 94 shows the spatial coexistence of multiple MACs.

FIG. 95 shows the mixing of two OFDM numerologies on the same carrier.

FIG. 96 shows a dynamic changing of portioning between two numerologies.

FIG. 97 shows a switching of link direction in TDD.

FIG. 98 shows options for beam shapes.

FIG. 99 illustrates an example CSI-RS allocation.

FIG. 100 illustrates a CSI-RS allocation for MU-MIMO operation.

FIG. 101 is a comparison between beam-based and coherentreciprocity-based modes, with respect to CSI acquisition signaling.

FIG. 102 is a simplified block diagram of a digital precoding-capableantenna architecture.

FIG. 103 illustrate an example of receiver processing.

FIG. 104 is a simplified block diagram of hybrid beamforming.

FIG. 105 is a block diagram illustrating analog precoding-capableantenna architecture.

FIG. 106 is a signaling flow diagram illustrating an active-modemobility procedure.

FIG. 107 is a signaling flow diagram illustrating beam selection basedon uplink measurement.

FIG. 108 is a signaling flow diagram illustrating intra-node beamselection based on uplink measurement.

FIG. 109 illustrates an example in which a UE detects a radio linkproblem and a serving node resolves the problem.

FIG. 110 shows use cases classified into three groups.

FIG. 111 depicts several use cases for self-backhaul.

FIG. 112 illustrates a device co-location perspective ofself-backhauling access nodes.

FIG. 113 shows a user-plane protocol architecture.

FIG. 114 shows a control-plane protocol architecture.

FIG. 115 shows a user-plane protocol architecture for LTE one-hoprelaying.

FIG. 116 shows a control-plane protocol architecture for LTE one-hoprelaying.

FIG. 117 shows a high-level architecture for L3 relay.

FIG. 118 shows routing versus PLNC.

FIG. 119 illustrates best-beam SINR variations over a UE route.

FIG. 120 illustrates several network scenarios.

FIG. 121 shows several UE types.

FIG. 122 illustrates MAC layer integration.

FIG. 123 shows RLC layer integration.

FIG. 124 shows PDCP layer integration.

FIG. 125 illustrates LTE-NX tight integration, built on RRC layerintegration.

FIG. 126 provides a summary of tight integration features.

FIG. 127 shows spectrum types and related usage scenarios for NX.

FIG. 128 illustrates problems with directional listen-before-talk.

FIG. 129 illustrates an example of a listen-after-talk mechanism.

FIG. 130 shows a PDCH-carried downlink data transmission.

FIG. 131 illustrates an example downlink data transmission.

FIG. 132 depicts an example uplink data transmission in cPDCH.

FIG. 133 illustrates an example uplink data transmission in PDCH.

FIG. 134 shows coupling between downlink and uplink grants.

FIG. 135 illustrates an example of SSI transmission.

FIG. 136 illustrates an example of SSI transmission contention.

FIG. 137 shows an example of AIT transmission.

FIG. 138 is a process flow diagram illustrating a UE access procedure inshared spectrum.

FIG. 139 is a process flow diagram illustrating management andautomation tasks for base station introduction.

FIG. 140 shows two system access regions with overlap, and nodes withinone system access region with and without overlap.

FIG. 141 illustrates UE BSID retrieval from a non-serving BS, to supportautomatic BS relations.

FIG. 142 is a signaling flow diagram showing BSID retrieval and TNLaddress recovery.

FIG. 143 is a signaling flow diagram showing uplink-based ABR.

FIG. 144 shows mobility beams and virtual mobility beams.

FIG. 145 illustrates virtual beam relations for the beams shown in FIG.144.

FIG. 146 illustrates virtual mobility beam relation establishment forgreenfield deployments.

FIG. 147 illustrates virtual mobility beam relation establishment formature deployments.

FIG. 148 shows virtual mobility beam relation establishment based on RLFreports.

FIG. 149 shows a re-establishment procedure initiated by a source BS.

FIG. 150 depicts a handover border scenario to illustrate a fasthandover procedure.

FIG. 151 illustrates geo-fence of a node.

FIG. 152 shows mobility load balancing in NX.

FIG. 153 illustrates tradeoffs for positioning requirements.

FIG. 154 illustrates central capabilities versus complexity.

FIG. 155 shows positioning components.

FIG. 156 illustrates an example of restricted PRS availability.

FIG. 157 is a signaling flow diagram illustrating support of restrictedPRS availability.

FIG. 158 shows positioning with a positioning support device.

FIG. 159 illustrates a categorization of D2D use cases.

FIG. 160 shows some D2D-related requirements in several use cases.

FIG. 161 illustrates D2D communications supported by the clusteringconcept.

FIG. 162 illustrates combinations of NX deployment scenarios and UEcapabilities.

FIG. 163 shows layer 2 switching of user data paths.

FIG. 164 illustrates a user plane protocol architecture for single hop.

FIG. 165 illustrates a user plane protocol architecture forUE-to-network relay.

FIG. 166 illustrates a user plane protocol architecture for UE-to-UErelay.

FIG. 167 shows control plane protocols used by D2D.

FIG. 168 shows some combinations of NX deployment scenarios and UEcapabilities.

FIG. 169 shows examples of sidelink management functions.

FIG. 170 shows examples of measurement functions desirable for D2Dcommunications.

FIG. 171 shows UE beamforming for D2D communications.

FIG. 172 shows an example sidelink scheduling operation.

FIG. 173 illustrates sidelink HARQ operation.

FIG. 174 depicts DRX alignment of infrastructure-to-device (I2D) and D2Dcommunications for maximizing OFF-duration.

FIG. 175 shows a D2D cluster communicating over cell borders.

FIG. 176 illustrates relations between different modes ofmulti-connectivity.

FIG. 177 shows a user-plane protocol stack for NX multi-connectivity.

FIG. 178 illustrates an alternative including one RRC entity at a MeNB.

FIG. 179 shows an alternative including multiple RRC entities at bothMeNB and SeNB.

FIG. 180 shows a fast MeNB and SeNB role switch procedure.

FIG. 181 is a block diagram illustrating an example wireless device.

FIG. 182 is a process flow diagram illustrating an example method in awireless device.

FIG. 183 is a process flow diagram illustrating an additional examplemethod in a wireless device.

FIG. 184 is a process flow diagram illustrating an additional examplemethod in a wireless device.

FIG. 185 is a process flow diagram illustrating an additional examplemethod in a wireless device.

FIG. 186 is a process flow diagram illustrating an additional examplemethod in a wireless device.

FIG. 187 is a process flow diagram illustrating an additional examplemethod in a wireless device.

FIG. 188 is a process flow diagram illustrating an additional examplemethod in a wireless device.

FIG. 189 is a block diagram illustrating example radio networkequipment.

FIG. 190 is a process flow diagram illustrating an example method inradio network equipment.

FIG. 191 is a process flow diagram illustrating an additional examplemethod in radio network equipment.

FIG. 192 is a process flow diagram illustrating an additional examplemethod in radio network equipment.

FIG. 193 is a process flow diagram illustrating an additional examplemethod in radio network equipment.

FIG. 194 is a process flow diagram illustrating an additional examplemethod in radio network equipment.

FIG. 195 is a process flow diagram illustrating an additional examplemethod in radio network equipment.

FIG. 196 is a process flow diagram illustrating an additional examplemethod in radio network equipment.

FIG. 197 is a process flow diagram illustrating an additional examplemethod in radio network equipment.

FIG. 198 is another representation of an example wireless device.

FIG. 199 is another representation of example radio network equipment.

DETAILED DESCRIPTION

Following are detailed descriptions of concepts, system/networkarchitectures, and detailed designs for many aspects of a wirelesscommunications network targeted to address the requirements and usecases for 5G. The terms “requirement,” “need,” or similar language areto be understood as describing a desirable feature or functionality ofthe system in the sense of an advantageous design of certainembodiments, and not as indicating a necessary or essential element ofall embodiments. As such, in the following each requirement and eachcapability described as required, important, needed, or described withsimilar language, is to be understood as optional.

In the discussion that follows, this wireless communications network,which includes wireless devices, radio access networks, and corenetworks, is referred to as “NX.” It should be understood that the term“NX” is used herein as simply a label, for convenience. Implementationsof wireless devices, radio network equipment, network nodes, andnetworks that include some or all of the features detailed herein may,of course, be referred to by any of various names. In future developmentof specifications for 5G, for example, the terms “New Radio,” or “NR,”or “NR multi-mode” may be used—it will be understood that some or all ofthe features described here in the context of NX may be directlyapplicable to these specifications for NR. Likewise, while the varioustechnologies and features described herein are targeted to a “5G”wireless communications network, specific implementations of wirelessdevices, radio network equipment, network nodes, and networks thatinclude some or all of the features detailed herein may or may not bereferred to by the term “5G.” The present invention relates to allindividual aspects of NX, but also to developments in othertechnologies, such as LTE, in the interaction and interworking with NX.Furthermore, each such individual aspect and each such individualdevelopment constitutes a separable embodiment of the invention.

NX, as described in detail below, targets new use cases, e.g. forfactory automation, as well as Extreme Mobile Broadband (MBB), and maybe deployed in a wide range of spectrum bands, calling for high degreeof flexibility. Licensed spectrum remains a cornerstone for NX wirelessaccess but unlicensed spectrum (stand-alone as well as license-assisted)and various forms of shared spectrum (e.g. the 3.5 GHz band in the US)are natively supported. A wide range of frequency bands are supported,from below 1 GHz to almost 100 GHz. It is of principal interest toensure that NX can be deployed in a variety of frequency bands, sometargeting coverage at lower frequency regions below 6 GHz, someproviding a balance of coverage, outdoor-to-indoor penetration and widebandwidth up to 30 GHz, and finally some bands above 30 GHz that willhandle wide bandwidth use cases, but possibly at a disadvantage tocoverage and deployment complexity. Both FDD and dynamic TDD, where thescheduler assigns the transmission direction dynamically, are part ofNX. However, it is understood that most practical deployments of NX willlikely be in unpaired spectrum, which calls for the importance of TDD.

Ultra-lean design, where transmissions are self-contained with referencesignals transmitted along with the data, minimizes broadcasting ofsignals. Terminals make no assumptions on the content of a subframeunless they are scheduled to do so. The consequence is significantlyimproved energy efficiency as signaling not directly related to userdata is minimized

Stand-alone deployments as well as tight interworking with LTE aresupported. Such interworking is desirable for consistent user experiencewith NX when used at higher frequency ranges or at initial NX rolloutwith limited coverage. The radio-access network (RAN) architecture canhandle a mix of NX-only, LTE-only, or dual-standard base stations. TheeNBs are connected to each other via new interfaces that are expected tobe standardized. It is envisioned that these new interfaces will be anevolution of the existing S1 and X2 interfaces to support features suchas network slicing, on demand activation of signals, UP/CP splits in theCN, and support for a new connected dormant state, as described herein.As described below, LTE-NX base stations may share at least integratedhigher radio interface protocol layers (PDCP and RRC) as well as acommon connection to the packet core (EPC).

NX separates dedicated data transmissions from system access functions.The latter include system information distribution, connectionestablishment functionality, and paging. Broadcast of system informationis minimized and not necessarily transmitted from all nodes handlinguser-plane data. This separation benefits beamforming, energyefficiency, and support of new deployment solutions. In particular, thisdesign principle allows densification to increase the user-planecapacity without increasing the signaling load.

A symmetric design with OFDM in both the downlink and the uplinkdirections is detailed below. To handle the wide range of carrierfrequencies and deployments, a scalable numerology is described. Forexample, a local-area, high-frequency node uses a larger subcarrierspacing and a shorter cyclic prefix than a wide-area, low-frequencynode. To support very low latency, a short subframe with fast ACK/NACKis proposed, with the possibility for subframe aggregation for lesslatency-critical services. Also, contention based access is part of NXto facilitate fast UE initiated access.

New coding schemes such as polar codes or various forms of LDPC codesmay be used, instead of turbo codes, to facilitate rapid decoding ofhigh data rates with a reasonable chip area. Long DRX cycles and a newUE state, RRC dormant, where the UE RAN context is maintained, allowfast transition to active mode with reduced control signaling.

Enabling full potential of multi-antenna technology is a cornerstone ofthe NX design. Hybrid beamforming is supported and advantages withdigital beam forming are exploited. User-specific beamforming throughself-contained transmission is advantageous for coverage, especially athigh frequencies. For the same reason, UE TX beamforming is proposed asan advantageous component, at least for high frequency bands. The numberof antenna elements may vary, from a relatively small number of antennaelements (e.g., 2 to 8) in LTE-like deployments to many hundreds, wherea large number of active or individually steerable antenna elements areused for beamforming, single-user MIMO and/or multi-user MIMO to unleashthe full potential of massive MIMO. Reference signals and MAC featuresare designed to allow exploiting reciprocity-based schemes. Multi-pointconnectivity, where a terminal is simultaneously connected to two ormore transmission points, can be used to provide diversity/robustness,e.g. for critical MTC, by transmitting the same data from multiplepoints.

NX includes a beam-based mobility concept to efficiently supporthigh-gain beam forming. This concept is transparent to both inter- andintra-eNB beam handover. When the link beams are relatively narrow, themobility beams should be tracking UEs with high accuracy to maintaingood user experience and avoid link failure. The mobility conceptfollows the ultra-lean design principle by defining a set of networkconfigurable down-link mobility reference signals that are transmittedon demand, when mobility measurements from the UE are needed. Techniquesare also described for up-link measurement based mobility, suitable basestations supporting reciprocity.

Access-backhaul convergence is achieved with access and backhaul linksusing the same air interface technology and dynamically sharing the samespectrum. This is particularly interesting at higher frequencies withlarge amounts of spectrum available, and where coverage is severelyhampered by physical and practical constraints. Device-to-devicecommunication where the network assigns resources for side-links ispreferably an integral part of NX. For out-of-coverage scenarios, theterminals revert to preassigned side-link resources.

5G MBB services will require a range of different bandwidths. At the lowend of the scale, support for massive machine connectivity withrelatively low bandwidths will be driven by total energy consumption atthe user equipment. In contrast, very wide bandwidths may be needed forhigh capacity scenarios, e.g., 4K video and future media. The NX airinterface focuses on high bandwidth services, and is designed aroundavailability of large and preferably contiguous spectrum allocations.

High-level requirements addressed by the NX system described hereininclude one or more of:

-   -   1) Support for higher frequency bands with wider carrier        bandwidth and higher peak rates. Note that this requirement        motivates a new numerology, as detailed below.    -   2) Support for lower latency, which requires shorter and more        flexible Transmission Time Intervals (TTIs), new channel        structures, etc.    -   3) Support for very dense deployments, energy efficient        deployments and heavy use of beam forming, enabled by, for        example removing legacy limitations in relation to CRS, PDCCH,        etc.    -   4) Support of new use cases, services and customers such as MTC        scenarios including V2X, etc. This can include more flexible        spectrum usage, support for very low latency, higher peak rates        etc.

Following is a description of the NX architecture, followed by adescription of the radio interface for NX. Following that is adescription of a variety of technologies and features that are supportedby the NX architecture and radio interface. It should be understood thatwhile the following detailed description provides a comprehensivediscussion of many aspects of a wireless communications system, wherenumerous advantages are obtained by combinations of many of thedescribed features and technologies, it is not necessary for all thetechnologies and features described herein to be included in a systemfor the system to benefit from the disclosed technologies and features.For example, while details of how NX may be tightly integrated with LTEare provided, a standalone version of NX is also eminently practical.More generally, except where a given feature is specifically describedherein as depending on another feature, any combination of the manytechnologies and features described herein may be used to advantage.

1 NX Architecture 1.1 Overview of Logical Architecture

The NX architecture supports both stand-alone deployments anddeployments that may be integrated with LTE or, potentially, any othercommunication technology. In the following discussion, there is a lot offocus on the LTE integrated case. However, it should be noted thatsimilar architecture assumptions also apply to the NX stand-alone caseor to integration with other technologies.

FIG. 1 shows the high level logical architecture for an example systemsupporting both NX and LTE. The logical architecture includes bothNX-only and LTE-only eNBs, as well as eNBs supporting both NX and LTE.In the illustrated system, the eNBs are connected to each other with adedicated eNB-to-eNB interface referred to here as the X2* interface,and to the core network with a dedicated eNB-to-CN interface referred tohere as the S1* interface. Of course, the names of these interfaces mayvary. As seen in the figure, a core network/radio access network(CN/RAN) split is evident, as was the case with the Evolved PacketSubsystem (EPS).

The S1* and X2* interfaces may be an evolution of the existing S1 and X2interfaces, to facilitate the integration of NX with LTE. Theseinterfaces may be enhanced to support multi-RAT features for NX and LTEDual Connectivity (DC), potentially new services (IoT or other 5Gservices), and features such as network slicing (where, for example,different slices and CN functions may require a different CN design), ondemand activation of mobility reference signals, new multi-connectivitysolutions, potentially new UP/CP splits in the CN, support for a newconnected dormant state, etc.

FIG. 2 shows the same logical architecture as FIG. 1, but now alsoincludes an example of an internal eNB architecture, including possibleprotocols splits and mapping to different sites.

Following are features of the architecture discussed herein:

-   -   LTE and NX share at least integrated higher radio interface        protocol layers (PDCP and RRC) as well as a common S1*        connection to packet core (EPC)        -   The RLC/MAC/PHY protocols in NX may differ from LTE, meaning            Carrier Aggregation (CA) solutions may, in some cases be            restricted to intra-RAT LTE/NX        -   Different options for how the RRC layer integration is            realized are discussed in section 2.        -   The usage of LTE or NX for 5G capable UEs can be transparent            to the EPC (if desired).    -   The RAN/CN functional split over S1* is based on the current        split used over S1. Note, however that this does not exclude        enhancements to the S1* compared to S1, e.g., to support new        features such as network slicing.    -   The 5G network architecture supports flexible placement        (deployment) of CN (EPC) functionality per user/flow/network        slice        -   This includes placement of EPC UP functions closer to RAN            (e.g., in a local GW) to allow for optimized routing and low            latency        -   It may also include EPC CP functions closer to RAN to            support stand-alone network operation (potentially all the            way to the hub site, as illustrated in FIG. 2).    -   Centralization of PDCP/RRC is supported. The interface between        PDCP/RRC and lower layer entities need not be standardized        (although it can be), but can be proprietary (vendor-specific).        -   The radio interface is designed to support architecture            flexibility (allowing for multiple possible functional            deployments, e.g., centralized/distributed).        -   The architecture also supports fully distributed PDCP/RRC            (as is the case with LTE, today).    -   To support NX/LTE dual connectivity with centralized PDCP and        RRC, NX supports a split somewhere between the RRC/PDCP layers        and the Physical layer, e.g., at the PDCP layer. Flow control        may be implemented on X2*, supporting the split of PDCP and RLC        in different nodes.    -   PDCP is split into a PDCP-C (used for SRBs) and PDCP-U (used for        URBs) part, which can be implemented and deployed in different        places.    -   The architecture supports CPRI-based splits between RU and BBU,        but also other splits where some processing is moved to the        RU/Antenna in order to lower the required fronthaul BW towards        the BBU (e.g., when supporting very large BW, many antennas).

Note that despite the above discussion, alternative RAN/CN splits arepossible, while still maintaining many of the features and advantagesdescribed herein.

1.2 UE States in NX and LTE 1.2.1 Introduction

This section discusses the different UE states in NX and LTE with focuson the UE sleep states. In LTE, two different sleep states aresupported:

-   -   ECM_IDLE/RRC_IDLE, where only the Core Network (CN) context is        stored in the UE. In this state, the UE has no context in the        RAN and is known on Tracking Area (or Tracking Area List) level.        (The RAN context is created again during transition to        RRC_CONNECTED.) Mobility is controlled by the UE, based on cell        reselection parameters provided by the network.    -   ECM_CONNECTED/RRC_CONNECTED with UE configured DRX. In this        state the UE is known on cell level and the network controls the        mobility (handovers).

Out of these two states, ECM_IDLE/RRC_IDLE is the primary UE sleep statein LTE for inactive terminals. RRC_CONNECTED with DRX is also used,however the UE is typically released to RRC_IDLE after X seconds ofinactivity (where X is configured by the operator and typically rangesfrom 10 to 61 seconds). Reasons why it may be undesirable to keep the UElonger in RRC_CONNECTED with DRX include limitations in eNB HW capacityor SW licenses, or other aspects such as slightly higher UE batteryconsumption or a desire to keep down the number of Handover Failures(KPI).

Since operators configure the RRC connected timer to be quite short,data from live LTE networks shows that UEs typically on average performten times more ECM_IDLE to ECM_CONNECTED state transitions than X2handovers, indicating that for many state transitions the UE returns inthe same eNB or cell as it was before. Data from live networks alsoshows that the majority of the RRC connections transfer less than 1Kbyte of data.

Given that initiating data transmission from ECM_IDLE in LTE involvessignificantly more signaling compared to data transmission from“RRC_CONNECTED with DRX”, the “RRC_CONNECTED with DRX” state is enhancedin NX to become the primary sleep state. The enhancement includes addingsupport for UE controlled mobility within a local area, thus avoidingthe need for the network to actively monitor the UE mobility. Note thatthis approach allows for the possibility that the LTE solution can befurther evolved to create a common RRC Connected sleep state for NX andLTE.

The following are features of this NX UE sleep state, which is referredto herein as RRC_CONNECTED DORMANT (or RRC DORMANT for short):

-   -   It supports DRX (from ms to hours)    -   It supports UE-controlled mobility, e.g., the UE may move around        in a Tracking RAN Area (TRA) or TRA list without notifying the        network (TRA (lists) span across LTE and NX).    -   Transition to and from this state is fast and lightweight        (depending on the scenario, whether optimized for energy saving        or fast access performance), enabled by storing and resuming the        RAN context (RRC) in the UE and in the network (see Section        2.1.5.6).

When it comes to detailed solutions how this RRC DORMANT state issupported, there are different options based on different level of CNinvolvement. One option is as follows:

-   -   The CN is unaware of whether the UE is in RRC_CONNECTED DORMANT        or RRC_CONNECTED ACTIVE (described later), meaning the S1*        connection is always active when UE is in RRC_CONNECTED,        regardless of sub state.    -   A UE in RRC DORMANT is allowed to move around within a TRA or        TRA list without notifying the network.        -   Paging is triggered by the eNB when a packet arrives over            S1*. The MME may assist the eNB by forwarding page messages            when there is no X2* connectivity to all the eNBs of the            paging area.        -   When the UE contacts the network from RRC DORMANT in a RAN            node that does not have the UE context, the RAN node tries            to fetch the UE context from the RAN node storing the            context. If this is successful, the procedure looks like an            LTE X2 handover in the CN. If the fetch fails, the UE            context is re-built from the CN.    -   The area that the UE is allowed to move around without notifying        the network may comprise a set of Tracking RAN Areas, and covers        both LTE and NX RAT, thus avoiding the need to signal when        switching RAT in RRC DORMANT.

In addition to the RRC DORMANT state (optimized for power saving), thereis an RRC_CONNECTED ACTIVE (RRC ACTIVE) state used for actual datatransmission. This state is optimized for data transmissions, but allowsthe UE to micro-sleep, thanks to DRX configuration, for scenarios whenno data is transmitted but a very quick access is desired. This may bereferred to as monitoring configuration within the RRC ACTIVE state. Inthis state, the UE cell or beam level mobility is controlled and knownby the network.

1.2.2 Consideration About UE States with Tight Integration of NX and LTE

Considering tight integration between NX and LTE, (see Section 2.7) thedesire to have a RAN controlled sleep state in NX drives requirements toalso support a RAN-controlled sleep state in LTE for NX/LTE capable UEs.

The reason for this is that to support tight NX and LTE integration, acommon S1* connection is desirable for LTE and NX. If a RAN-controlledsleep state is introduced on the NX side, it would be very beneficial tohave similar sleep state on the LTE side, also with an active S1*connection, so that the sleeping UE can move between NX and LTE withoutperforming signaling to setup and tear down the S1* connection. Thistype of inter-RAT re-selection between LTE and NX may be quite common,especially during early deployments of NX. Accordingly, a common RANbased sleep state called RRC_CONNECTED DORMANT should be introduced inLTE. The UE behavior in this state is similar to what is defined for LTERRC suspend/resume, however the paging is done by the RAN and not by theCN, since the S1* connection is not torn down when RRC is suspended.

Similarly, a common RRC_CONNECTED ACTIVE state between NX and LTE isdesirable. This state is characterized in that the NX/LTE capable UE isactive in either NX or LTE or both. Whether the UE is active in NX orLTE or both is a configuration aspect within the RRC ACTIVE state, andthese conditions need not be regarded as different sub states, since theUE behavior is similar regardless which RAT is active. To give oneexample, in the case only one of the links is active, regardless ofwhich link, the UE is configured to transmit data in one and to performmeasurements in another one for dual-connectivity and mobility purposes.More details are given in section 2.

1.2.3 Description of the NX/LTE States

FIG. 3 shows the UE states in an LTE/NX where LTE supports the commonRRC_CONNECTED ACTIVE and RRC_CONNECTED DORMANT states discussed above.These states are described further below.

Detached (Non RRC Configured)

-   -   EMM_DETACHED (or EMM_NULL) state defined in Evolved Packet        Subsystem (EPS) when the UE is turned off or has not yet        attached to the system.    -   In this state the UE does not have any IP address and is not        reachable from the network.    -   Same EPS state is valid for both NX and LTE accesses.

ECM/RRC_IDLE

-   -   This is similar to the current ECM IDLE state in LTE.    -   This state may be optional.        -   In the event this state is kept, it is desirable for the            paging cycles and Tracking RAN Areas to be aligned between            RAN-based paging in RRC DORMANT and CN-based paging in            ECM_IDLE, since then the UE could listen to both CN- and            RAN-based paging making it possible to recover the UE if the            RAN based context is lost.

RRC_CONNECTED ACTIVE (RRC State)

-   -   UE is RRC-configured, e.g., it has one RRC connection, one S1*        connection and one RAN context (including a security context),        where these may be valid for both LTE and NX in the case of        dual-radio UEs.    -   In this state it is possible, depending on UE capabilities, to        transmit and receive data from/to NX or LTE or both (RRC        configurable).    -   In this state the UE is configured with at least an LTE Serving        Cell or an NX serving beam and can quickly set up dual        connectivity between both NX and LTE when needed. The UE        monitors downlink scheduling channels of at least one RAT and        can access the system via for instance scheduling requests sent        in the UL.    -   Network controlled beam/node mobility: UE performs neighboring        beam/node measurements and measurement reports. In NX, the        mobility is primarily based on NX signals such as TSS/MRSs and        in LTE, PSS/SSS/CRS is used. NX/LTE knows the best beam (or best        beam set) of the UE and its best LTE cell(s).    -   The UE may acquire system information via SSI/AIT, for example,        and/or via NX dedicated signaling or via LTE system information        acquisition procedure.    -   UE can be DRX configured in both LTE and NX to allow        micro-sleeps (in NX sometimes referred as beam tracking or        monitoring mode). Most likely the DRX is coordinated between        RATs for UEs active in both RATs.    -   The UE can be configured to perform measurements on a non-active        RAT which can be used to setup dual connectivity, for mobility        purposes or just use as a fallback if the coverage of the active        RAT is lost.

RRC_CONNECTED DORMANT (RRC State)

-   -   UE is RRC-configured, e.g., the UE has one RRC connection and        one RAN context regardless of the access.    -   UE can be monitoring NX, LTE, or both, depending on coverage or        configuration. RRC connection re-activation (to enter RRC        ACTIVE) can be either via NX or LTE.    -   UE-controlled mobility is supported. This can be cell        re-selection in the case of only LTE coverage or NX Tracking RAN        Area selection in the case of NX-only coverage. Alternatively,        this can be a jointly optimized cell/area reselection for        overlapping NX/LTE coverage.    -   UE-specific DRX may be configured by RAN. DRX is largely used in        this state to allow different power saving cycles. The cycles        can be independently configured per RAT, however some        coordination might be required to ensure good battery life and        high paging success rate. Since the NX signals have configurable        periodicity there are methods that allow the UE to identify the        changes and adapt its DRX cycles.    -   UE may acquire system information via SSI/AIT in NX or via LTE.        UE monitors NX common channels (e.g., NX paging channel) to        detect incoming calls/data, AIT/SSI changes, ETWS notification        and CMAS notification.        -   UE can request system information via a previously            configured RACH channel.

2 Radio Interface: Functions, Procedures, Channels, and Signals

In this section the radio interface functions and services provided bythe different protocol layers, as well as preferred functional conceptsof the different layers are documented. In Section 2.1 the RadioResource Control (RRC) protocol is described, in section 2.2 the MAClayer is described, and, finally, in Section 2.3, the Physical layer isdescribed. Some RAN functions formally stretch over multiple layers butmay still be described in one section to simplify the presentation. Insome cases, the corresponding protocol aspects may be documented inSection 3.

2.1 Radio Resource Control (RRC) Protocol 2.1.1 Description

RRC is a signaling protocol used to configure and control the UE. RRCrelies on lower layers for security (encryption and integrityprotection), segmentation and reliable in-order delivery of signalingmessages. No detailed assumptions are made regarding when an RRC messageis delivered that makes the RRC messages asynchronous to the radiotiming. RRC is suitable for messages of any size requiring reliabledelivery such as UE configuration.

2.1.2 Functions Provided

Many of the same basic functions and procedures as defined in LTE RRCare also used in NX RRC, like security and connection control,measurement configuration, etc. However, new functionalities aredescribed herein. One new functionality is that the RRC protocol handlesboth NX standalone operation as well as NX and LTE joint operation,while keeping the NX and LTE related configurations of lower layersself-contained. Further design principles to realize the tightintegration from the RRC point of view are:

-   -   Fast state transition from dormant (see Section 1) to active        mode is provided. This is achieved by storing the UE context at        RAN.    -   Dormant state mobility is provided, where the UE is capable of        moving between RATs and nodes (within routing area) without        notifying the network.    -   RAN paging while in dormant mode is supported, across NX and        LTE.    -   Coordinated state transition where state transitions occur        jointly in both RATs is supported.    -   RRC signalling is optimized so that radio links on both RATs can        be established/moved/released at the same time.    -   The S1* connection can be sustained without any additional        connection setup when switching between LTE and NX,    -   Flexible procedures where both combined and independent        configuration (one layer) are supported. This can apply to        setup, mobility, reconfiguration and release of radio links.    -   The design is future-proof, so that new RRC functionalities        (e.g., to cover new use cases and support for network slicing)        can be added without major impact to the specifications.

Architectures that realize these design principles can be categorizedinto two options: Single RRC protocol and Dual RRC protocol, asdiscussed in Sections 2.1.4.1 and 2.1.4.2, respectively.

Other new functionalities of NX RRC include support for the new dormantstate, as discussed in Section 1, and new ways to deliver systeminformation, see chapter 3.2. Beam-based mobility management, asdiscussed in chapter 3.5, may drive additional changes. A new frameworkfor UE capability signaling is described in section 2.1.5.3.

RRC is involved in the Non Access Stratum (NAS) message exchange betweenUE and CN, and provides various control-plane functions both on UE andeNB:

-   -   Connection management:        -   RRC connection establishment, maintenance and release        -   RRC connection inactivation and re-activation        -   Radio bearer connection establishment, maintenance and            release        -   Multi-connectivity configurations        -   UE paging    -   UE capability transfer    -   Radio resource management:        -   Configuration of radio resources for RRC connection and            configuration of lower layers        -   Radio configuration control including e.g.,            assignment/modification of ARQ configuration, HARQ            configuration, DRX configuration        -   Measurement configuration and mobility control        -   UE measurement reporting and control of the reporting        -   Mobility functions (intra/inter-frequency handover, and            inter-RAT handover)        -   Radio Access Control, e.g., access class barring    -   Service management and security:        -   MBMS services        -   QoS management functions        -   Access Stratum (AS) security

The split architecture with RRC terminated in a centralized node, asdiscussed in Section 1, also impacts functions supported by RRC. Somefunctions are less suitable for a centralized implementation far fromthe air interface, for example:

-   -   Measurement reporting for beams. Measurement results supporting        intra node beam switching may be handled on a lower layer, see        section 2.1.5.8.    -   Air interface resources configured dynamically during        connections. In LTE, signaling of Physical uplink control        channel (PUCCH) resources when coming in-sync and TTI bundling        has been a problem.

2.1.3 Architecture 2.13.1 NX Identifiers Related to RAN L3 Procedures

There are several NX identifiers involved in RAN L3 procedures (inparticular RRC procedures), which are relevant to describe. Theseidentifiers may be critical for the procedure as such, or they may beidentifiers used by other layers or functions and simply transported bya RAN L3 message. The latter are of course less relevant to bring up inthis context, but in some cases they deserve to be mentioned.

Several circumstances motivate introducing new identifiers for NXinstead of merely reusing identifiers from LTE. Some of thesecircumstances are:

-   -   New functionality, which is non-existent in LTE, such as:        -   A new state, as in the dormant state.        -   RAN internal paging.    -   The lean design principle, which minimizes the data that is        frequently broadcast over the radio interface.    -   The heavy use of beamforming, which in practice eliminates the        traditional cell concept.    -   The potentially distributed RAN architecture.

Note that it is generally desirable to harmonize the RRC protocols forLTE and NX, and hence some of the related identifiers may be applicablein both LTE and NX.

This section provides an overview of such NX identifiers, elaboratingbriefly on aspects such as usage and internal structure.

The identifiers discussed here are each placed into one of twocategories:

-   -   UE identifiers    -   Network node, area or entity identifiers

2.1.3.1.1 UE Identifiers UE RRC Context Identifier

Reuse of the Cell Radio Network Temporary Identifier (C-RNTI) for thispurpose would not be suitable. One reason is that the cell concept isnot used in NX. Another reason is that the C-RNTI is coupled with otherfunctionality in a way that creates undesirable dependencies. A thirdreason is that the UE RRC context identifier has a partly differentpurpose in NX, such as to support context fetching.

The UE RRC context identifier identifies a UE's RRC context in the RANand hence it is unique within the entire RAN. In the case of a commonRRC entity the UE RRC context identifier is valid for both LTE and NX.The network can give the UE RRC context identifier to the UE at any timewhile the UE is in active state. The network may, for example, choose todo it in conjunction with the RRC connection setup (see section 2.1.5)when the context is created, in order to ensure that UE has it in caseit would lose the connection (e.g., in case of radio link failure).Alternatively, or in addition, the network may choose to transfer the UERRC context identifier to the UE when the UE is put in dormant state, toavoid the control overhead of having to reallocate a UE RRC contextidentifier in the UE every time the UE moves to a new RAN node.

The UE RRC context identifier is used for context fetching between RANnodes in potential procedures such as dormant to active state transition(see Section 2.1.5.6). Tracking RAN Area Update in dormant state andradio link failure recovery. It should identify a UE's RAN context in aninter-RAN node scenario. That is, it should both identify the RAN nodeholding the context (e.g., the “anchor node”, e.g., Access Node (AN),Radio Controller Function (RCF), or some other kind of controller suchas a cluster head) and identify the context within this RAN node. Hence,it comprises an identifier of the anchor RAN node and a local contextidentifier allocated by the anchor RAN node. The identifier of theanchor RAN node is the RAN node identifier described further below. Itcan be used also in other contexts and deserves its own separatedescription.

The local context identifier only has RAN node internal significance. Itcould be the MAC-id, which is used for addressing the UE for downlinkcontrol signaling, but in an ambition to retain independence betweenidentifiers that are used for different purposes, it is preferable thatthe local context identifier is an identifier separate from the MAC-id.In addition, the required range is different for the MAC-id and thelocal context identifier. Disregarding possible reuse schemes, theMAC-id range may provide a unique identifier to all UEs that aresimultaneously in active state in the applicable area (assumedly anAccess Node), whereas the local context identifier range may support allUEs that are in either active or dormant state in a node. The latter mayinclude a substantially greater number of UEs and hence a larger rangeis desirable for the local context identifier.

UE Identifier for RAN Internal Paging

For this purpose, there is no corresponding identifier to reuse fromLTE, since LTE does not support RAN internal paging.

The purpose of this identifier is to identify the UE when the UE ispaged during a RAN internal paging procedure. For RAN internal pagingthe UE is tightly associated with the already existing UE RRC context.This makes the UE RRC context identifier a natural candidate to be usedwhen paging the UE. Since this tight association makes it unlikely thatthe dependence to the UE RAN context identifier causes future problems,the UE RRC context identifier can be used for this purpose.

UE Identifier for the UE's Response to RAN Internal Paging

For this purpose, there is no corresponding identifier to reuse fromLTE, since LTE does not support RAN internal paging.

When the UE responds to RAN internal paging, it has to provide anidentifier that makes it possible to locate the UE RRC context. Areference to the page message, e.g., a page identifier, would suffice,but using a more “self-contained” identifier allows a more flexible pageprocedure, e.g., where the UE responds to a RAN node that has not beeninvolved in the paging. The relation to the UE RRC context makes the UERRC context identifier a natural candidate to be used for this purpose(especially since the page response may be regarded as dormant to activetransition).

UE Identifier for Dormant to Active State Transition

This is a new state transition, which does not exist in LTE and hencethere is no corresponding LTE identifier to reuse.

The UE's message to the network in conjunction with dormant to activestate transition has to enable location of the UE RRC context. Thismakes the UE RRC context identifier a natural candidate.

Summary of UE Identifiers

All of the above described identifiers (the UE RRC context identifier,the UE identifier for RAN internal paging, the UE identifier for theUE's response to RAN internal paging and the UE identifier for dormantto active state transition) may be one and the same, since all of themhave the ability to locate and identify a UE RRC context in an inter-RANnode scenario.

2.1.3.1.2 Network Node, Area or Entity Identifiers RAN Node Identifier

There are new features on the RAN node identifier which prevent reuse ofthe eNB ID in LTE.

A RAN node identifier to be visible across the radio interface is usefulfor various SON activities, such as Automatic Neighbor Relations (ANR)and recording of mobility in dormant/idle mode to aid radio networkplanning (see also section 3.9). (It is also possible to useRAN-node-specific MRSs for the purpose of ANR.) It is also useful in thenetwork for context fetching and establishment of inter-RAN nodeinterfaces and connections (e.g., X2*). Although a RAN node identifierin some senses corresponds to the eNB ID in LTE, the RAN node identifierin NX serves similar purposes in NX as the E-UTRAN Cell GlobalIdentifier (ECGI) does in LTE, due to the lack of cell concept in NX.

Two design goals that are relevant in this context are to minimize thealways-on transmissions in the network and to refrain from providingsignals that can be used for positioning purposes by over the top (OTT)applications.

To cater for the first of these two design goals, the RAN nodeidentifier may be transmitted over the radio interface on as-neededbasis. To this end, no RAN node identifier is transmitted over the radiointerface by default, but a RAN node may request the core network toorder activation (or the core network may initiate this itself) of RANnode identifier transmissions in a relevant area to support ANR or otherSON features. Optionally, the RAN node may indicate in the request whicharea it wants the RAN node identifier transmissions to be activated in,e.g., defined as a geographical area.

To fulfill the second design goal a dynamically assigned,non-systematically selected RAN node identifier is used across the radiointerface instead of a static RAN node identifier. To allow the dynamicRAN node identifier to still serve its purpose within the network, thenetwork provides (network internal) translation of the dynamic RAN nodeidentifier into an “actual” static RAN node identifier, which in turnmay be translated into an IP address if needed (or the dynamic RAN nodeidentifier may be used directly for IP address lookup). The approachwith network internal translation of a dynamically changed identifier issimilar to the approach described for the Positioning Reference Signal(PRS) (see section 3.10) and a common solution may be used for bothcases.

Tracking RAN Area Code

There are no Tracking RAN Areas in LTE and consequently there is noidentifier to reuse from LTE.

The Tracking RAN Area Code (TRAC) identifies a Tracking RAN Area (TRA)within a single network, to the extent that such areas are used. It maybe used in conjunction with configuration of a UE in dormant state witha list of TRAs and would be regularly transmitted by the network for theUE to keep track of its current TRA, and report location update to thenetwork if the UE moves to a TRA that is not in its configured list ofTRAs. As with the Tracking Area Code, no real need for any internalstructure is foreseen. See also section 3.2.

Phase Distributor for Paging DRX Cycles

In LTE, the IMSI modulo 1024 is used as an input parameter to the pagingoccasion procedure. Its purpose is to distribute the phase of the pagingDRX cycle among UEs, so that the accumulative paging load of the UEs ismore evenly distributed.

A parameter with a similar function may be desirable for the RANinternal paging in NX, depending on the procedure that is implementedfor paging occasions. Note that this is not an identifier per se, butwith the introduction of RAN internal paging it is a parameter thatmerits discussing.

Given that the same or a similar procedure as in LTE is used in NX, thenone approach is for the anchor RAN node (the RAN node holding the S1*connection) to generate a 10-bit number (the same number of bits as inIMSI modulo 1024) and configure the UE with it as a part of the pagingconfiguration for a UE in dormant state. This number would also beincluded in the RAN internal paging message distributed from the anchorRAN node to the other RAN nodes that are involved in paging the UE. Withthis choice of parameter, no IMSI related data is stored in the RAN.

An alternative is to derive this number from the UE RRC contextidentifier, e.g., UE RRC context identifier modulo 1024. This has anadvantage compared to an arbitrary 10-bit number in that it would nothave to be conveyed as a separate parameter to the UE and in thedistributed RAN internal paging message, since it would be implicit inthe UE RRC context identifier which is anyway included in thesemessages.

Yet another option is that the core network transfers the IMSI modulo1024 parameter to the RAN node as a part of the UE S1* context when theS1* connection is established and that this number is used in the samemanner as in LTE. If the same paging occasion procedure is used for RANinternal paging of a UE in dormant state and core network initiatedpaging of a UE in idle state, the paging occasions for RAN internal andcore network initiated paging coincide with this alternative. Thisproperty can advantageously be leveraged to efficiently deal with errorcases where the UE and the network have different perceptions of whichstate (dormant or idle) the UE is in.

Virtual Beam Identifier

This concept has no correspondence in LTE and consequently there is noLTE identifier to reuse.

A virtual beam identifier is an abstraction of a physical beam or agroup of physical beams. As such, it is adapted for use by inter nodesignaling procedures on the network side. The virtual beam identifier isinvolved in activation of candidate target beams in inter-RAN nodeactive mode mobility procedures and in SON procedures.

This identifier is used internally in the network (not passed to theUE).

Beam Identifier

This concept has no real correspondence in LTE, and consequently thereis no suitable LTE identifier to reuse.

A beam is identified on L1 by a certain, dynamically assigned referencesignal, e.g., a Mobility and Access Reference Signal (MRS). There may beno other identifier transmitted in the beam for beam identificationpurposes. However, higher protocol layers have to be able to refer to abeam, or a reference signal, e.g., when RRC is used to configure a UEwith the MRSs to measure on during a measurement sequence. For suchusage, the reference signal sequence itself is very impractical and ahigher layer abstraction is desirable instead. Hence, some kind ofreference or index is preferably used to refer to a reference signal,e.g., a MRS index or a C-RS index. Such an index may be passed betweenRAN nodes as well as between a RAN node and a UE.

PDCP Context Identifier

The PDCP context identifier is relevant in distributed RAN nodearchitecture scenarios where RRC processing and PDCP processing arelocated in different physical entities, e.g., with PDCP in a PacketProcessing Function (PPF) and RRC in a Radio Control Function (RCF)located in physically separate nodes. Such distributed RAN nodearchitectures are not standardized in LTE and hence there are no LTEidentifiers to reuse. (Note that a corresponding proprietary identifierin eNB products may be used, and in this case, if desired and unlesssuch an identifier is specified in NX, a product-specific/internalidentifier may be reused.)

To the extent that bearers are used in NX in a similar way as in LTE,with a PDCP context per bearer, then the bearer identifier incombination with a UE identifier (e.g., the UE RRC context identifier)may be used to identify a certain PDCP context.

Otherwise, if the bearer concept is replaced with something else, someother concept for the PDCP identifier is needed. In such a case the PDCPcontext identifier could be assigned according to similar principles asthe S1 connection identifier, where each entity assigns its ownidentifier and informs the other part. The PDCP entity would thus assignits own PDCP context identifier and inform the RRC entity after beingcontacted by the RRC entity.

If there is a one-to-one mapping between the RRC entity and the PDCPentity, then the PDCP context identifier can be used as the reference inboth directions, but if an RRC entity can have a relation to multiplePDCP entities, then the PDCP context identifier has to be combined withan RRC context identifier in order for it to uniquely identify theRRC-PDCP entity relation. The UE RRC context identifier can be reusedfor this purpose, and assuming that the distributed entities logicallyform a distinct RAN node (e.g., a “virtual RAN node”), the local contextidentifier part of the full UE RRC context identifier suffices. Notethat the terms “entity” and “context” should not be confused. In thisidentifier description an “entity” refers to a physical processingentity, e.g., an implementation of PDCP in a physical node. A “context”on the other hand refers to the data associated with a specific instanceof PDCP processing, e.g., for a certain bearer or traffic flow of a UE.

This identifier is used internally in the network (not passed to theUE). Note that the interface(s) that would motivate a PDCP contextidentifier are currently not standardized. Unless it becomesstandardized for NX, this remains a product internal matter and eachmanufacturer may choose what fits its specific implementation best.

Context Identifier for Lower Layer Protocols

Context identifiers for lower layer protocols may be relevant indistributed RAN node architecture scenarios, e.g., with RLC and MAC in aBaseband Function (BBF) and RRC in a Radio Control Function (RCF)located in physically separate nodes. In such a case, the RRC entity mayneed references to the relevant entities to be able to configure themappropriately. Such distributed RAN node architectures are notstandardized in LTE and hence there are no LTE identifiers to reuse.(There may, however, be a corresponding proprietary identifier in eNBproducts. In this case, if desired and unless such an identifier isspecified in NX, a product-specific/internal identifier may be reused.)

Assuming an LTE-like protocol stack, there is an RLC context per bearer,and its identifier could be treated in the same manner as describedabove for the PDCP context identifier.

The MAC entity, on the other hand, is common for all bearers of a UE,for each connectivity leg in case of dual-/multi-connectivity, so theMAC context identifier in principle only has to identify the UE and, asabove, the UE RRC context identifier, or the local part of it, could bereused for this purpose. These identifiers are used internally in thenetwork (not passed to the UE).

Note that the interface(s) that requires such identifier(s) is currentlynot standardized. Unless it becomes standardized for NX, this remains aproduct internal matter and each manufacturer may choose what fits itsspecific implementation best.

S1* and X2* Connection Identifiers

In LTE, an S1 connection identifier identifies an S1 control planeconnection associated with a UE and is valid as long as the UE is inRRC_CONNECTED and ECM-CONNECTED state (eNB UE S1AP ID, MME UE S1AP ID).(With the introduction of the suspend/resume mechanism in LTE release13, the S1 control plane connection may be kept also when the UE goes toRRC_IDLE state.) A corresponding X2 identifier identifies theshort-lived UE associated relation between two eNBs during a handoverprocedure (Old eNB UE X2AP ID, New eNB UE X2AP ID).

The same principle as currently used for S1 and X2, with locallyassigned and locally significant identifiers, may be used for the S1*and X2* connection identifiers. A similar reuse of the LTE principlesmay apply also for the S1* and X2* user plane identifiers. Theseidentifiers are used internally in the network (not passed to the UE).

Network Slice Identifier

A network slice identifier identifies a set of network resourcesconstituting a logical network. It may potentially be used to directuser plane and control plane traffic to the resources of the networkslice it pertains to.

2.1.3.1.3 Summary of Identifiers

Table 1, below, provides a summary of the identifiers discussed above.

TABLE 1 Identifier Purpose Relation to LTE UE RRC context Identifies aUE RRC It is slightly similar to the C- identifier context in the RAN.Used RNTI, but has a partly different e.g., for context fetching.purpose and lacks some of the dependencies associated with the C-RNTI.The UE RRC context identifier may identify the UE RRC context in bothLTE and NX. UE identifier for RAN Identifies a UE during Nocorrespondence in LTE internal paging RAN internal paging. UE identifierfor the Identifies a UE when No correspondence in LTE. UE's response toresponding to RAN RAN internal paging internal paging. Enables contextfetching. UE identifier for Identifies a UE during No correspondence inLTE. dormant to active dormant to active state state transitiontransition. Enables context fetching. RAN node identifier Supportsvarious SON New features prevent reuse of functions such as ANR. theeNode B ID. Enables context fetching when used as part of the UE RRCcontext identifier. Tracking RAN Area Identifies a Tracking Nocorrespondence in LTE. Code RAN Area. Phase distributor for Distributesthe phase of RAN internal paging is not paging DRX cycles the RANinternal paging used in LTE, but one option is (for RAN internal DRXcycle among UEs, to reuse the IMSI modulo 1024 paging) so that theaccumulative parameter which is used for paging load of the UEs is corenetwork initiated paging in more evenly distributed. LTE. Virtual beam Avirtual beam identifier No correspondence in LTE. identifier is anabstraction of a physical beam or a group of physical beams. Beamidentifier A beam identifier is used No suitable correspondence in toidentify a physical LTE. layer beam on higher protocol layers. It may berealized as an index pointing at a reference signal sequence. PDCPcontext Used to identify the To the extent the bearer identifier PDCPcontext in a concept of LTE is reused in distributed RAN node NX, thebearer identifier architecture. combined with the UE RRC contextidentifier may be used. Otherwise only product internal/specificcorresponding identifiers may be used. Context identifier for Used toidentify the RLC To the extent the bearer lower layer protocol contextor the MAC concept of LTE is reused in context in a distributed NX, thebearer identifier RAN node architecture. combined with the UE RRCcontext identifier may be used (or only the UE RRC context identifier inthe case of the MAC context). Otherwise only product internal/specificcorresponding identifiers may exist. S1* and X2* Identify control anduser The same principle (and connection plane connections for possiblythe same identifiers) identifiers S1* and X2*. can be used as in LTE.Bearer identifier Identifies a (radio) To the extent the LTE bearerbearer. (if needed, concept is reused in NX, the depending on the LTEbearer identifier may existence of bearers possibly be reused. in NX.)Network slice Identifies a set of network No correspondence in LTE.identifier resources constituting a logical network.

2.1.3.2 Signaling Radio Bearers

Signaling Radio Bearers (SRBs) are defined as Radio Bearers (RB) thatare used only for the transmission of RRC and NAS messages. According tothe architecture described herein, the same set of SRBs may be definedfor NX as used for LTE. This also allows the tight integration scenario,where the same SRBs are used to carry either NX or LTE RRC messages overeither NX or LTE lower layers (see Section 1).

More specifically, the following three SRBs may be defined:

-   -   SRB0 is for RRC messages using a common logical channel;    -   SRB1 is for RRC messages (which may include a piggybacked NAS        message) as well as for NAS messages prior to the establishment        of SRB2, all using dedicated logical channels;    -   SRB2 is for RRC messages which include logged measurement        information as well as for NAS messages, all using dedicated        logical channels. SRB2 typically has a lower-priority than SRB1        and is configured by E-UTRAN after security activation.

Once security is activated, RRC messages on SRB1 and SRB2, includingthose containing NAS or non-3GPP messages, are integrity protected andciphered by PDCP.

It is also important to note that RRC diversity can be supported byutilizing a common SRB1 and SRB2, which can be split over both RATs,similarly to the split dedicated radio bearers (DRBs) used in LTEDual-Connectivity (DC), using a common PDCP entity with separate RLC/MACentities per access. The UE or network does not apply RRC diversity forSRB0 as well as for the initial SRB message sequence during the initialconnection setup or connection re-establishment/re-activation until bothRATs are configured and security activated. Once SRB diversity isactivated, implementation-based dynamic link selection in the downlinkcan be made by the network on a per PDCP PDU basis. In the uplink,mapping rules may be defined in the standard.

Using a common set of SRBs with a split bearer is an attractive option,since that guarantees in-order delivery of all RRC messages regardlessof over which RAT they are transmitted (the UE behavior becomespredictable). When a common PDCP layer is used, supporting solutions fortransmitting the same RRC message over both RATs becomes easy, since anyduplication can be detected and removed by the PDCP layer.

An alternative solution is to use separate SRBs for different RATs, andthen have rules in RRC level for when messages should be mapped to whatSRB. One option is to define an NX specific SRB3, which is then used forNX RRC for procedures that do not need to be coordinated with LTE RRC.This entity is used in the non-co-located case located in the NX eNB todeliver NX RRC messages directly between the NX eNB and the UE, withouthaving to be passed via the LTE eNB. Note that from a security point ofview, this solution deviates from the DC architecture with a singletrusted node terminating all SRBs. Here, the secondary eNB needs to beequally trusted and securely implemented as the master eNB. Otherwise anattacker breaking into the secondary eNB could control the UE via RRCfrom there.

2.1.3.3 Bearer Handling and QoS

As for the SRBs, the tight integration with LTE motivates keeping commonradio bearers also for the user plane, allowing the UE to move betweenLTE and NX coverage without having to reconfigure the bearers.

However, new use cases for 5G may drive the introduction of new QoSdefinitions for NX, and new bearer types. Ideally, those should then beintroduced to LTE as well, so that seamless LTE-NX mobility can besupported. In cases where LTE is not capable to provide the requiredQoS, bearers need to be reconfigured or released when moving from NX toLTE.

2.1.3.4 Handling of DRX in Dormant State

DRX is configured together with paging and the “listening period”iscalculated based on the current System Frame Number (SFN). Each TRA mayhave a specific DRX configuration which is provided to the UE viadedicated signaling e.g., TRA Update Response or RRC reconfiguration.The range of DRX cycles which the network can configure goes up toseveral hours or even days. Of course, this needs to be taken intoaccount when designing the number of bits to include in the SFN field.

In some cases, the RAN may not be able to find the UE. In thissituation, the RAN may inform the CN, and the CN may then take over thepaging functionality for that UE.

One aspect to take into account is the relationship between SSI (seesection 3.2.2.2) period and DRX configuration. Longer SSI periods causehigher UE energy consumption, due to the effect of the UE clock error incombination with DRX. The UE needs to wake up before to compensate forthis error. As soon as the UE gets sync information, the UE can returnto DRX. Thus, the longer the SSI period (time from one SSI transmissionto the next), the longer the UE needs to listen and, hence, the higherthe UE energy consumption. Shorter SSI periods, on the other hand, causeless UE power consumption. This is shown in FIG. 4, which illustratesestimated UE battery life for a UE in dormant state when the network issynchronized for different SSI period and DRX cycles. When the networkcannot maintain a good level of synchronization, the UE energyconsumption increases considerably, especially for large SSI periods.This is shown in FIG. 5, which illustrates estimated UE battery life fora UE in dormant state when the network is not synchronized for differentSSI periods and DRX cycles.

2.1.4 NX RRC and Integration with LTE

A preferred aspect of the architecture described herein is its supportfor a tight integration of NX with LTE, e.g., as discussed in Section3.7. One part of this tight integration is the RRC layer integration ofLTE and NX radio access, to support both the LTE-NX dual connectivityand NX stand-alone operation. In this section, several differentalternatives for realizing this RRC layer integration are described,starting from RRC functional concepts.

2.1.4.1 RRC Functional Concept 1: Single RRC Protocol

Single RRC protocol is defined as a protocol architecture option, whichcan integrate all or a subset of the control-plane functions of NXtogether with the existing LTE RRC protocol functions with a single RRCprotocol machine, to provide the functions to enable the LTE-NX dualconnectivity and possibly the stand-alone NX operation.

Note that this architecture option can be realized by extending the LTERRC protocol. This can be achieved by standardization of:

-   -   a) a new release for the LTE RRC specification, TS 36.331,        including the new procedures and information elements (IEs) for        NX, or    -   b) a new specification, e.g., an NX RRC specification that        contains the LTE RRC legacy functions, new procedures and IEs        for NX, or    -   c) a pair of specifications comprised of a new release of the        LTE RRC specification, including transparent containers for        carrying NX IEs, which are defined in a new NX RRC        specification.

The NX IEs, which can be defined within the LTE RRC specification or ina separate NX RRC specification, may include broadcasted/dedicatedsystem information and security control information elements.

Where an RRC function (e.g., RRM) resides in the NX eNB, new inter-nodemessages (e.g., carrying radio resource control information elements)between NX and LTE have to be defined. These messages are carried withinthe RRC containers that need to be specified as well.

To ensure the reliable handling of the control-plane signaling, PDCPlevel split/combining can be used to provide extra reliability (RRCdiversity).

Note that in the case of stand-alone NX operation, due to thebackward-dependency of the protocol, single RRC protocol may havelimited flexibility when adding new functions to NX RRC, especially if asingle RRC evolution track for both LTE and NX is targeted.

An overall protocol stack that includes single RRC operation for LTE-NXDC operation is illustrated in FIG. 6, from the UE and eNB perspectives,respectively. The node where the RRC and PDCP entities reside may beeither an LTE or NX node.

2.1.4.2 RRC Functional Concept 2: Dual RRC Protocol

Dual RRC protocol refers to a protocol architecture option comprisingseparate LTE and NX RRC entities, which follow independent control-planespecifications for LTE and NX respectively. Inter-RAT coordination ismandated in the RRC level, to fulfil the LTE-NX tight integration designprinciple.

With this architecture option, future-proof NX control-plane functionsare provided for the stand-alone operation of NX and for the smoothintroduction of new features and use cases, thanks to the functionalflexibility introduced with less backward-dependency.

In the dual RRC protocol, NX RRC messages are tunneled to the UE via theLTE RRC entity and vice-versa for LTE-NX dual connectivity, which is thecase whether LTE and NX RATs are co-located or not. Therefore, the RRCcontainers that carry the NX/LTE RRC messages need to be specified.Furthermore, in order to sustain a single S1 connection and coordinatedstate transitions between NX and LTE, additional mechanisms may berequired as partly to be discussed within the RRC procedures.

Similarly as with the single RRC protocol option, PDCP levelsplit/combining (for common SBRs), via a single PDCP entity on thecontrol-plane, is assumed to enable RRC diversity and reliable handlingof control-plane thereof. An additional PDCP entity (for new SRBs),associated to an NX SRB, e.g., SRB3, can also be configured in the NXnode for the direct NX RRC message transfer when the common PDCP entityis situated in the LTE node.

An overall protocol stack that includes the dual RRC operation isillustrated in FIG. 7, from the UE's and eNB's perspectives,respectively.

2.1.5 RRC Procedures

FIG. 8 illustrates an overall RRC signaling diagram for LTE-NX dualconnection setup, where the dashed lines indicate the involvement of RRCsignaling associated with NX (independent from the RRC protocolarchitecture options).

2.1.5.1 Initial RRC Connection Signaling

Initial RRC signaling includes RRC Connection Request (SRB0) and RRCConnection Setup/Reject (SRB0), and RRC Connection Setup Complete/AttachRequest (SRB1) message sequence.

As discussed in Signaling Radio Bearers (Section 2.1.3.1), the same setof SRBs may be defined for NX as used for LTE. This also allows thetight integration scenario, where the same SRBs are used to carry eitherNX or LTE RRC messages (or both messages if both are to be set up) overeither NX or LTE lower layers. The initial connection signaling may alsobe reused between LTE and NX.

At the initial RRC connection setup procedure, the UE can select whichRAT to perform access based on a predefined criterion. During the RRCconnection setup procedure, the UE may be assigned an UE RRC Context ID(see section 2.1.3.1.1) that is kept when the UE goes to dormant stateor updated via an RRC connection inactivation signaling as to bediscussed.

To activate the tight integration features, a UE can be indicated asLTE+NX UE within the Attach request, when UE moves from RRC IDLE to RRCCONNECTED mode. Subsequently, the UE can be configured for dual RATconnectivity with a single RRC reconfiguration procedure, as discussedin section 2.1.5.4.

2.1.5.2 Security Signaling

FIG. 9 illustrates a security setup for LTE and NX, assuming a commonMME connection.

Given the use of a common set of SRBs for LTE and NX with common PDCPentities, separate security configuration for LTE and NX controlsignaling is not required. If the SRB3 described in 2.1.3.2 isconfigured, however, a separate security configuration would be requiredfor that.

Security setup can be optimized by using common capability signalling,single authentication, single key generation and common security modecommand as shown, for example, in FIG. 9. The common security setup caneither be handled by the single RRC or dual RRC protocol architectureoption. In case of dual RRC, the LTE header indicates the transparentcontainer for NX RRC messages. In either architecture, a single PDCPentity can provide a common encryption (as in LTE DC operation) as wellas integrity protection for common SRBs. It is also possible toimplement a separate PDCP entity, enabling new NX SRBs.

2.1.5.3 UE Capability and Related Signaling

For NX, a new UE capability signaling framework addresses limitations ofthe 2G/3G/LTE UE capability signaling. More particularly, the new UEcapability signaling framework addresses one or more of the followingissues:

-   -   Fixed set of capabilities: A UE typically indicates supported        features. However, features may be a compound of several        building blocks and may have different parameters. These may not        have all been tested or be fully functional, though. Thus, it is        desirable that the UE can report more capabilities/building        blocks/allowed configurations once they are tested.    -   Network vendor inter-dependencies: By industry practice,        features are tested in at least two network (NW) vendors, prior        to activation of the features at the UE. To address specific        markets/operators/devices or UE-network specific features, it is        desirable to avoid such NW inter-dependences.    -   Faulty UEs: Once a UE is released into the market, it is        difficult to fix implementation errors, as it is complicated to        identify faulty UEs. Network work-arounds are usually introduced        when a major issue is found, and these work-arounds typically        apply to all the UEs within the release in which the fault was        found.    -   Proprietary implementations: No framework exists today to        introduce proprietary features/building blocks/configurations or        other proprietary enhancements between a network and a UE.    -   Continuous increase of UE capabilities: As system specifications        evolve, the UE capabilities increase, which has a direct impact        in the radio interface as well as in the exchange of information        within the network nodes.

A new UE capability framework that addresses these issues includes oneor both of the following two elements:

-   -   UE capability pointer/index: This is a pointer/index that the UE        sends to the network. This pointer identifies all possible UE        capabilities and other relevant information for that particular        UE, and even for the UE capabilities relevant to a specific        network vendor.    -   UE capability database: A UE capability database contains all        the information corresponding to each of the pointers. This        database is maintained in another location, e.g., central node,        3^(rd) party, etc. Note that this database may contain more        information than merely UE capability information. It could        potentially be customized for each network vendor, e.g., tested        features/configurations, fault reports, proprietary UE-NW        information, etc. It is, therefore, important that        network-specific information is not accessible by others and is        protected/encrypted.

FIG. 10 illustrates features of the UE capability framework describedabove.

2.1.5.4 RRC Connection Reconfiguration Signaling

RRC Connection Reconfiguration message can establish/modify/releaseradio bearers, configure L1, L2 and L3 parameters and procedures (e.g.,for mobility and/or to establishment of dual connectivity).

In case of stand-alone NX, RRC Connection Reconfiguration message can beused for single NX connection reconfiguration (similarly to theLTE-equivalent message) as well as for NX multi-connectivity setup asdiscussed in Section 3.13.

In case of LTE-NX dual connectivity setup, the RRC connectionreconfiguration can be either be network-triggered or UE-triggered.

In the case of network-triggered procedure two options are described.

When the single RRC architecture option is assumed, a common RRCprotocol (e.g., as specified in a future NX release of 3GPP TS 36.331)is responsible for the dual LTE-NX connectivity connection setupprocedures. In this case, the RRC connection reconfiguration procedurefor LTE and NX can be handled within a single-round of RRC messageexchange as shown in FIG. 11. IEs containing the NX configuration arecarried in the Setup Response.

FIG. 11 thus illustrates the LTE-NX dual connectivity setup used withthe single RRC protocol architecture, where the illustrated signaling isbased on the assumption that the first node is an LTE eNB. The signalingother way around, where the first node is an NX eNB, would follow thesame message sequence.

In case of the dual RRC option, there is more than one way to realizeLTE-NX dual connectivity setup.

In one alternative, one of the RRC protocols can handle the RRCconnection reconfiguration procedure, allowing the NX/LTE dualconnectivity configuration in a single round of reconfiguration. This isshown in FIG. 12. This can be done by using the existing PDCP entity andassociated security in the node where the control-plane (either LTE orNX) is up and running. The RRC messages of the second RAT may betransferred to the UE via the first RAT within a transparent containeror directly to the UE via new SRB, such as SRB3. FIG. 12 illustratesLTE-NX dual connectivity setup for use with the dual RRC protocolarchitecture with a common RRC reconfiguration procedure. Theillustrated signaling is based on an assumption that the first node isan LTE eNB. The signaling the other way around, where the first node isan NX eNB, would follow the same message sequence.

2.1.5.5 RRC Connection Inactivation

This procedure handles the state transition from RRC CONNECTED ACTIVE toDORMANT, which effectively puts the UE to “sleep” in LTE and/or NX. Thetransition can be triggered due to a timer configured by the network orby an RRC Connection Inactivation message sent by the network, which mayinclude the security re-activation information (e.g.,nextHopChainingCount) for the next RRC CONNECTED ACTIVE state. Uponreceiving this message, the UE enters the RRC DORMANT state. Given adual RRC for LTE and NX, the message should be defined in both RRCspecifications, e.g., using similar IEs.

Some of the UE RRC configuration in RRC CONNECTED DORMANT could beconfigurable by the network during the RRC connection setup,inactivation, and re-activation procedures, within which the UE RRCContext Identity can also be assigned. The network also ensures that theinformation for the UE dormant behavior is up to date. This informationis especially important in the NX case where the system information iseither not broadcasted (e.g., dormant mode mobility parameters) orseldom broadcasted (e.g., AIT, see section 3.2.2.2).

Updated configuration may also be given to the UE in the RRC ConnectionInactivation message, since the UE may have moved to a location with adifferent dormant state configuration. Other changes to the informationin the RRC Connection Inactivation message may be made. For instance,the UE could be configured to camp on MRSs (see Section 3.4.4 forfurther details) and re-active the connection accordingly. The networkcould also mandate the UE to keep the MAC identities and associate sometimers when moving to dormant.

Upon entering the RRC DORMANT state (without any additionalconfiguration for optimized state transition), the UE should:

-   -   Release all radio resources including the release of the RLC        entity and the MAC configuration, e.g., including a release of        the MAC-Id.    -   Keep all PDCP entities (common for both LTE and NX) of SRBs and        RBs and the RRC UE Context Identity (see Section 2.1.3.1.1) that        is received in the RRC Connection Setup (either over NX or LTE        RRC in the case of dual RRC). This identity encodes both the        context identifier and the mobility anchor point in the RAN        which can be e.g., an LTE cell ID or NX node Id.    -   Camp in the same RAT (NX or LTE) it was active (default) unless        some specific configuration is provided. For increased        robustness, dual-camping is also an option, as discussed in        Section 3.2.

2.1.5.6 RRC Connection Re-Activation

In LTE, latency requirements for the transition from RRC IDLE to RRCCONNECTED have been defined. In Release 8 of the LTE specifications,transition latencies <100 milliseconds (ms) were targeted from a campedstate. In the case of a transition from sleeping state (Connected DRX)to active, the target was 50 ms. In Release 10 of the LTEspecifications, requirements were further reduced to <50 ms and <10 ms(excluding DRX delay). These values are to be further reduced for 5G,especially considering some critical service that may have highrequirements in terms of latency.

From an RRC perspective, to minimize the overhead and achieve a lowerlatency, a lightweight transition is provided, as shown in FIG. 13. Ifthe UE has received the security re-activation information such asnextHopChainingCount in RRC Connection Inactivation, a subsequent RRCreconfiguration procedure is not needed, since the RRC connectionre-activation procedure would be able to reconfigure SRBs and DRBsactivating the user plane thereof.

FIG. 13 illustrates a signaling flow for RRC connection re-activationprocedure, assuming that the first node is an LTE eNB. The signalingother way around, the first node is NX eNB, follows the same messagesequence.

The purpose of RRC connection re-activation procedure is to re-activatethe RRC connection, which involves the resumption of SRBs and DRBs. Theconnection re-activation succeeds only if the accessed target node (NXor LTE) can find the UE RRC context and the mobility anchor for S1*. Forthis reason, the UE RRC Context ID is included within the RRC ConnectionRe-activation Request that is an SRB0 message. This message can beintegrity protected to protect the network from the false requests.

The procedure for instance, may be triggered by the UE either inresponse to a paging, when the UE has UL data in buffer, or when itneeds to send TRA updates. The UE triggers an RRC connectionre-activation procedure, which should be defined in both NX and LTE'sRRC specifications when a dual RRC solution is implemented.

Upon receiving RRC Connection Re-activation Request, the networkretrieves the UE RRC Context (including the security re-activationinformation) based on the UE RRC Context ID, performs the necessarymobility actions and responds with RRC Connection Re-activation toreconfigure SRBs and DRBs. Upon reception of this message, the UEperforms the following actions:

-   -   Re-establishes PDCP and RLC for SRBs and DRBs,    -   Performs radio resource configuration,    -   Performs measurement related actions according to the        measurement configuration,    -   Resumes SRBs and DRBs.

2.1.5.7 Measurement Configuration

Several different types of measurements and/or signals are measured inNX (e.g., MRS, SSIs, TRAS, etc.). Mobility events and procedures thusneed to be addressed for NX.

The RRC Connection Reconfiguration message should be able to configureboth the NX measurements and the existing LTE measurements for thesingle RRC option. The measurement configuration should include thepossibility to configure the UE to measure for NX/LTE coverage e.g., toinitiate DC setup or inter-RAT HO (as in the legacy).

2.1.5.8 Measurement Reporting

There are two different measurement reporting mechanisms for NX, non-RRCbased reporting (see Section 2.3.7.2), where the UE indicates the bestof a set of candidate DL beams through a preconfigured USS sequence; andRRC-based reporting, which is similar in some respects to theevent-triggered LTE measurement reporting. These two measurementreporting mechanisms are preferably deployed in parallel and usedselectively, e.g., depending on the UE's mobility state.

2.1.6 System Information

System information as known from previous releases of the LTE standardsconsists of very different types of information, access information,node-specific information, system-wide information, public warningsystem (PWS) information, etc. Delivery of this wide range ofinformation does not use the same realization in NX. In a system withhigh-gain beamforming, the cost of providing large amount of data inbroadcast manner may be costly compared to point to point distributionin a dedicated beam with high link gain.

2.1.6.1 Desirable Features & Principles

Desirable features and design principles for NX include one or more ofthe following. Thus, it should be appreciated that not necessarily allof these may be met by a given implementation.

-   -   NX should support a “flexible” mechanism to convey System        Information        -   Restrictions on System Information length should be avoided        -   System Information parameter values may be modified at any            time        -   System Information may take advantage of parameters which do            not change or are common across a large area        -   System Information may carry different information for            different types/groups of UE and or services        -   Dedicated signaling should be considered when more efficient        -   Efficient signaling to thousands (e.g., 512 k) of UEs per            “service area” should be supported.    -   NX should minimize broadcasted information and “always-on-air”        -   Network DTX should be supported    -   Acquisition/updates should minimize:        -   the impact to UEs to which information is not addressed        -   the negative side effects in the network e.g., synchronized            UL accesses        -   the contribution in the UE battery consumption    -   Acquisition/updates should not:        -   Increase access (until “relevant info” is retrieved) latency            by more than xx* ms (e.g.: at initial power on, roaming            (PLMN search), after RLF (recovery), redirected to a new            layer/cell, handover, inter-RAT, “long” DRX cycles), System            Information Update (*exact latency feature may depend on            service/type/group of UE)    -   “Relevant” information should be unambiguous and “up-to-date”        prior usage        -   It may be acceptable that “outdated” info is used if the            probability is very low/system impact negligible    -   System information coverage range should not be dependent of the        user plane coverage range        -   e.g., a node may not transmit system information while it            may transmit user plane data    -   System Information should be conveyed efficiently for all type        of deployments        -   NX as standalone with minimum and/no coverage overlap        -   NX should be able to be deployed stand-alone on unlicensed            bands        -   NX deployed with a LTE/UTRAN/GERAN with full or partial            coverage        -   Dual NX layer deployment, NX macro and NX small cells, two            scenarios:            -   Where the UE is in coverage of both the macro cell and                the small cell simultaneously            -   Where the UE is not in coverage of both the macro cell                and the small cell simultaneously    -   Secondary carriers may not need to provide SI (e.g., LAA,        dedicated frequency)    -   Each node may dynamically change/update some of its System        Information        -   System Information changes/updates may not be coordinated            and may not be populated among other nodes/layers in all            cases    -   System Information should handle/consider handling of:        -   Shared networks        -   Mobility        -   (PWS) Public Warning Systems        -   A mechanism (e.g., paging) to request the UE to:            -   a) to contact the NX or, b) acquire System Information            -   Should be possible to address to groups/types of                UEs/services        -   MBMS function        -   Load sharing and policy management between NX and other RATs        -   Access control (updated feature)            -   NX should comply with SA features (e.g., as in 3GPP TS                22.011)            -   Access control information may be available on a node by                node basis            -   Access control in “connected” should be possible to                configure for types/groups of UE and/or different                services

2.1.6.2 System Information Acquisition

System information acquisition for NX standalone operation is detailedin Section 3.2.

In tight integration operation with LTE, system information acquisitionresembles, in some respects, that of dual connectivity for LTE. Assumingthe UE accesses LTE first and then activates NX, the UE receives the NXsystem information in dedicated transmission, via the LTE RRC, whensetting up the NX connection. In LTE DC, this applies to all systeminformation, except SFN acquired from MIB of the Primary Serving Cell(PSCell) of the SCG. For NX, the SFN may be included in the TRAS (seesection 3.2.4.1.3). The same principle applies to the other way around:a UE accessing NX first and then activating LTE obtains the LTE systeminformation in dedicated transmission via the NX RRC.

2.1.7 Paging

The paging solution for NX utilizes one or both of two channels: aPaging Indication Channel, and a Paging Message Channel.

Paging Indication Channel (PICH)

The paging indication may contain one or more of the following: a pagingflag, warning/alert flag, ID list, and resource allocation.

Paging Message Channel (PMCH)

PMCH may optionally be transmitted after the PICH. When the PMCH messageis sent, it may contain one or more of the following contents: ID list,and warning/alert message. Warning and broadcast messages are preferablyto be transmitted over the PMCH (and not in the AIT).

To allow tight integration with LTE, paging configuration (and so DRXconfiguration) is SFN-based.

To support paging functionality, tracking RAN areas are configured atthe UE. A tracking RAN area (TRA) is defined by a set of nodestransmitting the same tracking RAN area signal (TRAS). This signalcontains the Tracking RAN Area Code as well as the SFN.

Each TRA may have a specific paging and TRAS configuration which isprovided to the UE via dedicated signaling, e.g., via a TRA UpdateResponse or RRC Reconfiguration message. The TRA Update Response may,furthermore, contain paging messages. More information on paging can befound in Section 3.2.

2.1.8 Establishment of LTE-NX Dual Connectivity

In section 2.1.5.4, network-triggered establishment of LTE-NX dualconnectivity is described using the RRC reconfiguration procedure. Inthe example given, the UE has an RRC connection towards the network andRRC messages are exchanged using the LTE eNB. As in the other RRCprocedures described in section 2.1.5.4, the higher layers (theasynchronous functions, e.g., RRC/PDCP) can be common to LTE and NX.Upon the reception of measurement reports over the LTE link (e.g.,containing NX measurements) the network decides upon the establishmentof dual connectivity with NX by sending a RRC connectionre-configuration message, containing the necessary information for theUE to establish a link towards NX. This message can be seen as a commandto the UE to establish a connection towards the secondary eNB (SeNB).

Another scenario is a UE-initiated procedure, where the UE directlycontacts NX to establish LTE-NX dual connectivity. An example of thisapproach is shown in FIG. 14. Benefits of accessing NX directly includea lower latency procedure and some additional level of diversity (e.g.,when the first link is unstable). Assume the UE has an RRC connectionwith the network and uses the link from one of the RATs, e.g., LTE, toexchange RRC messages. The UE then initiates the access towards asecondary RAT (e.g., performing synchronization and random access overNX) and sends via the secondary RAT link (e.g., NX) an RRC messagecontaining a UE context identifier (e.g., the UE RRC context identifierdescribed in section 2.1.3.1) indicating the request to establish dualconnectivity. This context identifier contains the location of theanchor point, so that upon the reception of that message the secondaryRAT can locate the single control point at the network from where the UEis controlled. After the network figures that out (e.g., via X2* in anon-collocated scenario) it sends an RRC message to the UE to configurethe NX resources for the existing SRBs/DRBs (previously established overLTE) and/or the configuration of novel NX SRBs/DRBs associated to NX.The same applies for the measurement configurations. The UE-initiatedprocedure can be applied either for the single or dual RRC case,however, it may be more useful in the dual RRC case where one couldpossibly have a different RRC reconfiguration procedure over thesecondary RAT (NX, in the present example). Note that the fact that thisalternative is called UE-initiated does not mean that it isUE-controlled. What triggers the UE to send the request towards thesecondary node (NX in the example given) may be an event configured viaRRC by the network.

2.2 Layer 2 Design for NX

The NX architecture and details disclosed herein address one or more ofa number of problems with LTE, such as the following: LTE uses a fixedHARQ feedback timing which is a problem in some implementation scenarios(e.g., with centralized baseband deployment or non-ideal backhaul) andwhen operating in unlicensed spectrum (e.g., where listen-before-talksometimes prevents UEs from sending HARQ feedback); the LTE UL and DL L1control channels can be improved for better support of high-gainbeamforming, as the switches between transmission modes andconfigurations is unnecessarily hard and slow; there can be a ratherlong latency coming from the UL scheduling; the DRX behavior is notalways optimal; and the design of the scheduling request channel is notas flexible or efficient as desired, for all applications.

In addition, support for reciprocal massive MIMO transmission andmassive MIMO beamforming can be made to work better in NX than in LTE.Other improvement areas are one or more of dynamic TDD; unlicensed bandoperation; contention-based access; multi-connectivity; multi-hop; D2Detc. NX can provide native and optimized support for increasinglyimportant use-cases such as multi-X (multi-connectivity, multi-RAT,multi-hop, multi-carrier, multi-node, multi-beam), UL/DL decoupling,etc.

To handle expected and unexpected migrations in the service mix, allradio links in NX are capable of operating within a bounded set of radioresources (resource slice), thus avoiding that terminals makeassumptions on or rely on signals outside these resources. The trafficscenarios supported by NX range from a single 100-bit packet every hourall the way up to multiple Gbps continuous data transfers. The frequencyrange to be supported is much wider, ranging from below 1 GHz up to 100GHz. There are wide assumptions on device and node capabilities (e.g.,from 1 to 400 antennas, from hours to 20-year battery life, etc.).

2.2.1 Design Principles—Impact on L2 Design

Design principles for the Layer 2 (L2) design of NX are detailed below.

Service agnostic design allowing flexible service centricconfigurations: Different use-cases have vastly diverse requirements.For example, some C-MTC use-cases need extreme reliability with BLER inthe order of 10⁻⁹; tactile internet services need very low end-to-endlatency of 1 ms; extreme MBB benefit from multiple Gbps of userthroughput, etc. The NX standard provides a large set of serviceagnostic features which the network may configure and enable to fulfillthe service specific requirements. This enables co-existence of multipleservices while maintaining low complexity and high efficiency for eachservice.

Stay in the box: An important feature of LTE is that all traffic ismapped dynamically to a single pair of shared channels (PDSCH/PUSCH).This maximizes statistical multiplexing and allows a single UE to getinstantaneous access to all radio resources of a carrier or evenmultiple carriers. Appropriate RLC configurations and schedulingpolicies ensure that QoS requirements are met. While NX maintains thisfundamental principle, some services just cannot be multiplexed. Forexample, it is not acceptable if a braking command in a traffic junctionis interfered by a packet from the entertainment system in a nearby car.Hence for some critical use cases (e.g., intelligent transport system,public safety, industrial automation, etc.) it may not be acceptable tocoexist on the same radio resources with any other service. For thispurpose, certain services may be operated on dedicated time andfrequency resource slices of the radio spectrum. Separating the radioresource in this manner also enables lower complexity implementation andtesting in some situations. If a service becomes deprecated in oneparticular area (e.g., a factory is closed down) then that spectrum canbe quickly reassigned to another service, by managing the resourceslices assigned to different services. The default assumption is thatall services shall be able to coexist on the same carrier but usingdedicated resource slices is a solution for support of so-calledvertical services. Thus, in NX, any service can be contained within adefined set of radio resources.

Flexibility: NX has a lean and scalable design that is able to cope withvarious latencies on the transport and radio interface as well as withdifferent processing capabilities on UE and network side. To ensurethis, fixed timing relations are avoided between control messages suchas HARQ (MAC), ARQ (RLC) and RRC signaling.

Design for flows: For NX, control signaling may be optimized byutilizing correlations in traffic. This avoids hard and slowreconfigurations. Whenever a future behavior can be predicted (e.g.,something sent in the downlink there will be uplink traffic a shortwhile later) the L2 design may take advantage of that: e.g., start withopen-loop transmission and do a seamless switch to a closed-looptransmission format once the channel state information becomes availableat the transmitter end.

Layers of coordination: When the cost of observation and control becomestoo high, e.g., in terms of delay or overhead, scheduling decisions aredelegated to nodes and UEs for the time it takes to collect sufficientinformation and enforce a suitable coordination. The centralizedresource scheduler still owns and controls the right to use radioresources but in situations where observation and control is easier andmore efficient to maintain in another node (e.g., in multi-hop relayingor D2D), the momentary decisions on how to assign resources can bedistributed.

Lean and thereby future-proof: The mandatory transmissions to be done byan NX eNB at specific times are sparse in time and frequency. Forexample, the NX terminal should not expect control messages at specifictime/frequency resources (as is the case today for HARQ feedback inLTE). The configurability enables forward compatibility as the networkcan assign resources freely to other (newer) terminals without having tosend a massive amount of legacy signals for legacy terminals. Inparticular, when operating in unlicensed spectrum, the NX radiointerface may send control information at dynamic time instances. Inaddition to containing all signals in a bounded resourced slice, a userequipment should be capable of ignoring any “un-defined resources”within the resource slice unless explicitly instructed otherwise.“Un-defined resources” may be dynamically configured as a set ofperiodic patterns in time, and/or in frequency.

2.2.2 L2 Channel Structure

For NX, the defining of separate control channels for different purposesis avoided except where absolutely necessary. The main reason for thisis to optimize the design for massive MIMO and high-gain beamforming.Separate channels have a tendency to rely on frequency diversity as wellas separate demodulation reference signals and the resource space canquickly become cluttered. Once a good channel is established towards aspecific UE, e.g., by means of a very large number of antennas, it ismuch more efficient to use this also for transmitting controlinformation.

This is in line with the stay in the box design principle describedabove. Furthermore, this is based on an observation that whentransmitting user data in one link there are often transmissions in thereverse link as well.

Furthermore, any service should be able to be delivered within a boundedset of radio resources (a resource slice), thus avoiding a design whereL1 control channels and reference signals are spread out over the entiresystem bandwidth. To enable this, the L2 channel structure supportsin-band control information, with different channel encoding,modulation, HARQ configuration, etc.

2.2.2.1 Direct and Re-Transmittable Physical Data Channel (PDCH)

NX achieves flexibility and scalability by being a system that supportsmore than one physical channel. Rather than having different kinds ofchannels for control and data, channels may be regarded as being eitherdirect or re-transmittable. In this document, a direct channel isdenoted dPDCH and the re-transmittable channel is denoted rPDCH. Thestructure of having a direct and a re-transmittable channel is equallyapplicable to both uplink and downlink transmissions. The differencebetween such channels is that they may be optimized for differentoperational points. The direct channel may, e.g., be designed for a BLERof 10⁻³ without soft HARQ combining, while a re-transmittable channelmay target 10% BLER and support several HARQ retransmissions with softcombining in the receiver. Note that here we are referring to channelsfor processing Layer 2 (L2) data.

Some information, like downlink control information (DCI) or channelquality information (CQI) feedback may only be relevant if the eNB candecode it upon the first transmission attempt while other type of data,such as user-plane data or RRC control messages, benefit from successfuldelivery even if that requires multiple HARQ re-transmissions. Onesingle channel structure, optimized slightly differently, caters forboth of these very different needs. Note that in some cases theuser-plane data may require much lower error probability than L1/L2control signaling (e.g., up to 10⁻⁹ for C-MTC and 10⁻³ for L1/L2 MBBrelated control signaling) and in such scenarios we may either make useof two direct channels or one that is configured for the highestrequirements. Compared to LTE, a difference with this structure is thatwe assume there is no need for designing tailored channels for specialkinds of L1/L2 control information. In-band control multiplexed withdata transmissions is the default assumption.

One may think of this as having a direct and a re-transmittable channelwhere time-critical information is mapped to the former while other datais mapped to the latter. In general, whether a channel isre-transmittable or not is just a parameter setting and not afundamental difference in design. Therefore, the channels can bereferred to with just a number, such as 1 and 2, for example, indicatingthat they just happen to have different configurations. In the examplesprovided, the differently configured channels may be used for differentpurposes. To support different services, different numbers of physicalchannels may be used. Since the network decides how to fill a downlinktransport block, what MCS to use, and whether or not to performretransmissions, such a scheme could alternatively be realized with asingle channel.

FIG. 15 illustrates how a MAC control element, such as a CSI report oran UL grant, can be mapped to a direct or re-transmittable channel. Itshould be appreciated that whether to transmit any given informationelement on a low-delay optimized (and more expensive, generally) directchannel or on a high-spectral-efficiency re-transmittable channel is ascheduler decision in NX.

Note that even if the majority of the control information is in-beam,some kind of physical layer control channel is still desirable. Inaddition to the data channel, a bootstrapping resource that, e.g., canbe used to schedule an initial channel use, is desirable. For thispurpose, a physical downlink control channel (PDCCH) is defined, wherethe UE receiver blindly searches for the PDCCH in a pre-defined orsemi-statically configured search space. The usage of this PDCCH isdepicted in FIG. 16. Note that it is possible to use this physicalcontrol channel more or less as in the current LTE system, e.g., it canbe used every TTI to schedule DL and UL transmissions. However, animportant use of the PDCCH in the NX context is to support a shifttowards having a larger part of the dedicated user data and theassociated L1/L2 control information transmitted with aggressivebeamforming.

As illustrated in FIG. 16, the PDCCH is used in NX to enable high gainbeam-forming and in-beam transmission of control information. The PDCCHis designed to be robust and simple and has a separate set ofdemodulation reference signals in order to support a different(typically wider) beamforming than the PDCH.

Because relying on very high-gain beamforming for the data channel alsoincreases the risk of radio-link failures, a more robust fallbackchannel is desirable. For that reason, the PDCCH for NX is designed tobe lean and simple. In order to quickly resume transmission in thisfallback scenario, the PDCCH is very robust and optimized for a widercoverage area. This implies lower antenna gain and higher cost per bit.But, this enables the majority of the control information to be sent“in-beam”.

The PDCCH also enables transmission of control information before CSI isavailable, e.g., as an initial bootstrap channel. Since the transmissionof control information on the PDCCH is typically more expensive (due tothe lower beam-forming gain), only a limited set of simple DCI formatsare supported, containing only a small number of bits. This is not arestriction in practice, since without CSI and during the very beginningof a transmission burst (e.g., during the TCP slow start), advancedprocedures that requires a lot of control information are not performedanyway.

UE multiplexing on a shared control channel requires a number of blinddecoding attempts. But, by not using the PDCCH as much, the overallnumber of blind decoding attempts that the UE needs to perform isreduced. Most UEs receive their control information in-beam on the“directly decodable” data channel, most of the time, which gives bettercontrol of how to multiplex control information to different UEs.

Note that new DCI formats may be added only to the in-beam “directlydecodable” channel and not on the PDCCH, in some cases. This makes itpossible to extend the control channel functionality in NX withoutchanging the shared PDCCH. More specifically, NX can be extended in amanner where new DCI formats are added only to the dPDCH and not thePDCCH.

2.2.2.2 Relation Between PDCCH and dPDCH

Above, two different control channels for the downlink are described,PDCCH and dPDCH. The main different between these two channels is thatthe dPDCH uses the same demodulation reference signal as the datachannel (rPDCH) while the PDCCH uses a different DMRS. Both the PDCCHand the dPDCH/rPDCH can be beam-formed towards the UE. Both the PDCCHand the dPDCH/rPDCH can also be transmitted in a wide beam or with adiversity based beam-former.

The PDCCH is primarily designed to be used when very accurate CSIinformation is not available in the base station, such that the basestation cannot perform reciprocity-based beamforming. The PDCCH uses aDMRS that is typically shared by multiple UEs. It is designed to relymore on frequency diversity than on antenna diversity and can thereforebe used in NX deployments with a small (e.g., 2 or 4) number ofantennas.

The dPDCH/rPDCH channels are primarily designed for supportingreciprocity-based beamforming and dynamic TDD (UL RRS based). In thisscenario, DL DMRS are not needed in theory, but in practice downlinkdemodulation reference signals may also be used in this case, sinceperfect and absolute UL/DL calibration is not practical.

The PDCCH, on the other hand, does not rely on UL reciprocity referencesignal (RRS). It is time-multiplexed with dPDCH/rPDCH in order tosupport hybrid beam-forming. One reason why the messages on the PDCCHshould be small is that otherwise experience coverage problems of thischannel may be a bottleneck in higher frequency bands. If coverage ofthe PDCCH on high frequency bands is a concern, then PDCCH can beprovided only on a lower frequency band, with the dPDCH/rPDCH being usedon a higher frequency band. The transmission of UL RRS on the highfrequency band that enables reciprocity based beamforming of dPDCH/rPDCHcan then be controlled by the PDCCH on the low frequency band.

As described further in the next section below, there is a difference inhow the search space is used on the PDCCH and dPDCH as well. The searchspace on PDCCH supports user-multiplexing, link-adaptation, andrate-adaptation. The search space of the dPDCH, on the other hand, doesnot need to support user-multiplexing.

2.2.2.3 Dynamic Search Space

FIG. 17 illustrates, on the left-hand side, how the PDCCH may be used todynamically update the DCI search space in the UE. The middle portion ofFIG. 17 shows that there is no need to send a search update to the UEwhen not changing the start location of the DCI search space. On theright-hand side, FIG. 17 shows that when changing starting location ofthe dPDCH (the UE DCI search space), a forward DCI is used. This maycause error propagation

It can be seen that the bottom portion of FIG. 17 depicts the case wherea DCI is received in-beam, on a scheduled resource. This can be enabledby extending the UE search space for downlink control information toalso include resources that need to be dynamically scheduled. In theleft part of FIG. 17, the UE receives a DCI₀ on the PDCCH, which pointsout where to start searching for additional control information. In thedirectly decodable part of the assigned resource (dPDCH), the UE mayfind the control information relevant for this TTI (DCI,). In thisexample the PDCCH schedules only the search space extension and not theactual DCI.

The middle part of FIG. 17 indicates that the UE may continue to searchin the same location, for multiple TTIs. The actual physical datachannel assignment may move without enforcing the dynamic search spaceof the UE to be changed. The UE may still perform a number of blinddecoding attempts in order to enable rate and link adaptation of thedPDCH.

A new DCI need only be sent when changing the location of the dPDCH.This is depicted in the rightmost part of FIG. 17. Since this DCIimpacts what happens in the next TTI, there is a risk of errorpropagation in the event that the UE cannot receive the “forward DCI”containing the search space extension information.

When DCI information conveying information on where to search for ULgrants and future DL assignments is embedded into the PDCH, then theerror propagation cases that might occur need to be considered. Theerror propagation cases are in many situations easily detected by thenetwork, and they occur only when the UE DCI search space is updated.Some of them are depicted in FIG. 18. In the top part of the figure isshown the error-free operation of this “DCI-daisy chain” operation. Moregenerally, FIG. 18 shows examples of possible error propagationscenarios when using in-band DCI to update the UE search space.So-labeled boxes indicate the usage of a bootstrap channel (e.g., PDCCHor a contention-based physical data channel), lightly-shaded boxesindicate a directly decodable PDCH, while more darkly-shaded boxesindicate a re-transmittable PDCH.

In the event that the UE does not receive the dPDCH, it does not receivethe embedded UL grant. When the NW detects that the scheduled ULtransmission from the UE is missing, it can be assumed that also thenext DL assignment was missed. These failed assignments can bedistinguished from failed UL transmission by energy detection, e.g.,SINR estimate on DMRS, UL transmission contain data but not HARQfeedback. Error propagation can be further mitigated by introducing“control information received acknowledgment” when search space ischanged. As a response, the NW may re-transmit the DCI for the second DLTTI using the PDCCH. This is depicted in the middle part of FIG. 18.

In the event that the UE expects to receive an UL grant but does notreceive any, then it might use a pre-scheduled contention-based resourceinstead. The use of a contention-based uplink channel instead of ascheduled dedicated channel is an indication that the first dPDCHdecoding has failed (see bottom part of FIG. 18).

In addition to the implicit error propagation detection mechanismsdepicted in FIG. 18, the network may also request the UE to sendexplicit and event triggered reports on the detection success of dPDCHtransmissions. An example of this is shown in FIG. 19, which shows thatwhen scheduled in the UL, the UE can report back the reception successof the dPDCH in previous TTIs. Depending on the performance of in-beamDCI, this extra level of error-propagation termination might not benecessary, in a given implementation.

The search space for downlink control information (DCI) is thusdynamically updated by means of DCI signaling. The DCI may betransmitted directly on a downlink physical control channel (PDCCH) orembedded in a MAC control element inside a scheduled downlink datachannel (typically the dPDCH).

UE search space modifications such as add/delete/move may be signaledexplicitly, e.g., in a previously received DCI or MAC control element.The search space modifications may also be implicit, e.g., byautomatically extending the UE search space to include locations usedfor DCIs in the previous N Ills or by automatically delete the oldest UEsearch space location when a new search space location is added.

2.2.2.4 Shared Reference Signals

The use of in-beam control channels relies on having the same dedicateddemodulation reference signal (DMRS) for both the dPDCH and the rPDCH.This is shown in FIG. 20, which illustrates an example of using a singleset of terminal specific demodulation reference signals (four shadedregions having 8 resource elements each) for demodulation of twophysical channels, the dPDCH and the rPDCH.

At a first glance, the illustration in FIG. 20 looks similar in somerespects to how in LTE the CRSs are used as common reference signals fordemodulation of PDCCH and PDSCH. However, there are differences.Although the CRSs in LTE may be beamformed, e.g., by down-tilting of theantenna, the beamforming cannot be changed dynamically with respect to aparticular UE, since there are other UEs measuring on the CRSs. Thus,when using ePDCCH+DMRS on PDSCH in LTE, two sets of reference signalsare used, leading to higher pilot overhead. When CRS-based transmissionin LTE (PDCCH+PDSCH TM4) is used, then there is no option of dynamicallybeam-forming the reference signals towards the receiving user.

2.2.2.5 Resource Partitioning

In LTE, the total system bandwidth is signaled on the PBCH. For NX, itis not assumed that a user is aware of the system bandwidth. A notion ofa user-specific bandwidth is still desirable, e.g., for channelfiltering and signaling purposes. The BW that a UE is operating withinis here defined by a “resource partition”. A resource partition is atime-and frequency subset of radio resources in which we can defineradio links and transmission modes. One property of a resource slice isthat it can be semi-statically re-configured (which in not the case forthe “system bandwidth” in e.g., LTE).

This implies that all modes of transmission that are defined for NX areable to operate on a subset of the time/frequency resources. Suchsubsets, or resource partitions, span dimensions from full utilizationdown to a minimum utilization. Note that this also includes allTM-specific reference signals. These restrictions in time and frequencyare semi-static—they are configured by RRC.

2.2.3 Transport Channels

An NX radio link can thus have one or more physical data channels (e.g.,dPDCH and rPDCH) in each direction (UL and DL) and the scheduling entityalso has access to a physical control channel (PDCCH) used fortransmitting control information only. The MAC structure of eachphysical channel is the same for UL and DL. An example with two PDCHs,the first one having 1 transport block (TB) and the second one havingtwo transport blocks is depicted in FIG. 21. Each channel has a MACHeader and a payload part containing MAC Elements. The MAC elements areeither Control Elements or MAC SDUs (service data units).

FIG. 21 shows the basic MAC channel structure of NX. A lean and simpleboot-strap channel denoted physical control channel (PDCCH) is used toinitiate a packet exchange flow. A first or “directly decodable”physical channel (denoted dPDCH) carries primarily in-band controlinformation. A second or “re-transmittable” physical data channel(denoted rPDCH) carries primarily user-plane and control-plane data.Both physical data channels are assumed to re-use the transport channelstructure of LTE.

The content of the MAC sub-headers are, in principle, the same as forLTE today. The sub-header can consist of 1, 2, or 3 bytes ofinformation. The structure [R/R/E/LCID] is used for fixed length MACSDUs and fixed length MAC Control Elements, and the structure[R/R/E/LCID/F/Length] is used for variable length MAC SDUs and ControlElements. This is shown in FIG. 22, which shows how the transportchannel structure and MAC-header format from LTE is re-used also for NX.

In LTE, the logical channel ID (LCID) is defined in separate tables forUL and DL. NX follows the same general approach. FIG. 23 shows examplesof how the LCID tables can be updated for UL and DL, where someadditional LCIDs in NX are shown. For the DL, one addition is to supportthe transmission of a DCI (downlink control information) as a MACcontrol element. The DCI can, just as in LTE today, be used to assign anUL grant, schedule a DL transmission, or to send a power-controlcommand. In addition, the DCI is extended to also support a command fortransmission of reference signals, such as UL reciprocity referencesignals (RRS), denoted RS transmission command in FIG. 23. Alsoinformation about reference signal transmissions, e.g., to supportactive mode mobility with dynamically activated and beam-formedreference signals, can be communicated in a DCI. This can be included ina RS transmission information element in FIG. 23. Note that thedifferent kinds of DCI may also be encoded as separate LCID fields. Forthe UL there is no similar UCI field defined, and instead the differentkinds of UL control information each have their own LCID field.

In addition to DCI and UCI, transmission of HARQ feedback in a MACcontrol element is enabled. This in turn enables introduction of newfeedback schemes such as selective repeat or schemes where more than onefeedback bit per process is used. Also, a LCID for CSI feedback isintroduced as well as an entry for reference signal measurementfeedback. Note that not all LCIDs are relevant in all cases. Some aremostly relevant in the DL while some are mostly relevant for the UL.

In FIG. 24 is shown a downlink example in which two PDCHs areconfigured. The figure shows a downlink channel structure examplecomprising a physical control channel (PDCCH), a first “directlydecodable” physical data channel (dPDCH) and a second “re-transmittablephysical data channel (rPDCH). The dPDCH does not use soft combining ofHARQ re-transmissions and it can only carry a single transport block(TB₁) while rPDCH does support HARQ and supports transmission of up totwo transport blocks (TB₂ and TB₃). In addition, the downlink PDCCH cantransmit DCI and possibly also some other MAC-control elements embeddedinto one transport block TB₀. The UE identity is implicitly (orexplicitly) encoded in the CRC of the downlink PDCCH. Note that adifference between the downlink PDCCH and any of the PDCH channels isthat the downlink PDCCH cannot carry any MAC SDUs. Furthermore, thedownlink PDCCH is blindly decoded by the UE while the PDCH channels arescheduled (implicitly, semi-persistent or dynamically).

A corresponding example for the uplink is depicted in FIG. 25, whichillustrates an uplink channel structure example comprising a physicalcontrol channel configured for contention-based access (cPDCH), a firstdynamically scheduled “directly decodable” physical data channel (dPDCH)and a second dynamically scheduled “re-transmittable physical datachannel (rPDCH). Note that the uplink does not have any scheduler butinstead a priority handler entity that selects data from the logicalchannels and controls the MAC Multiplexing within the grants provided.Since there is no scheduler, there is no need for any PDCCH channeleither. Instead, the UL transmitter has a channel cPDCH that isprimarily intended for contention-based use. A difference between cPDCHand the other two uplink physical data channels (dPDCH and rPDCH) isthat they are granted differently.

The contention-based channel (cPDCH) uses a semi-persistent grant thatmay be assigned also to other UEs. Therefore, the UE identity is encodedonto the channel (implicitly in the CRC or explicitly using a MACControl Element with LCID 11000; see FIG. 23) whenever cPDCH is used. Inthe event that the UE does not have a sufficiently sized grant, it maysend a scheduling request (e.g., a buffer status report) on cPDCH.Depending on the size of the grant on the “contention-based channel”cPDCH, the UE may also include user-plane data when transmitting on thatchannel. Note that channels carrying system access information andsignals such as the PRACH are not included in the illustrated structurein FIG. 25. Should the UE not have a valid grant for any channel, thentransmitting a PRACH pre-amble is an alternative (see section 3.2 forfurther details).

The “direct channel” (dPDCH) and the “re-transmittable channel” (rPDCH)may be scheduled in a dynamic fashion. When using granted resources onthese channels, it is assumed that the receiver knows who istransmitting, and hence no UE identity needs to be embedded.

Note that these are just examples used to illustrate that the basic PDCHstructure in FIG. 21 works for both UL and DL, for a typical mobilebroadband use case. For other use cases, the UL and DL radio links maybe configured slightly differently, e.g., without any second“re-transmittable” data channel. By granting resources in differentmanner and by embedding user identities on some channels and not onother channels, many different use cases can be supported.

For the uplink, note that all non-system access related channels arescheduled in some manner (semi-persistent; dynamic; or implicit).So-called contention-based channels are not special in any particularway. Whether a resource is “dedicated” or not becomes irrelevant in somescenarios, e.g., when massive MIMO or high-gain beamforming is used toenable spatial multiplexing. When resources can be spatially separated,time/frequency resources need to be “dedicated,” and consequently thereceiver in the base station should be able to derive who thetransmitter is. On contention-based channels a UE identity is embeddedin the channel, while on dedicated channels this is not needed. The ideahere is that different physical channels have different properties.Different channels may use different sub-sets of a large commontransmission format table (e.g., different channel encoders). Continuingwith the example in FIG. 25, for instance, three PDCHs may be configuredas follows:

-   -   cPDCH: Optimized for “contention use”. For example, a small        grant may be available every 2 ms for transmissions of a buffer        status report when needed. The UE is allowed to not use this        grant. Normally, if a UE is scheduled on the UL and has no data        to transmit, it needs to fill the granted resource with padding        but for this channel the UE may simply refrain from transmitting        anything at all in that case. The grant may also have a        restriction (e.g., can mostly be used 10 consecutive times) and        possibly a cool-down timer (e.g., not allowed to use during 100        ms after the grant is exhausted). The channel encoder may be        configured to be a small block code. A “UE identity” and a        packet sequence number needs to be signaled when this channel is        used.    -   dPDCH: Does not support soft-combining of re-transmissions; uses        robust transport formats; optimized for embedded control        information such as “HARQ feedback”, “CSI feedback”, and “RS        measurement feedback”.    -   rPDCH: Carries 1 or 2 transport blocks of uplink data; uses        soft-combining of re-transmissions based on HARQ-feedback;        optimized for efficient transport of MAC-SDUs (user data).

2.2.4 Scheduling

Resource allocation can be simplified in NX, especially when the nodesare equipped with many antennas. This is due to so-called channelhardening, which essentially means that after the application of anappropriately chosen precoder to the transmitted signal, the effectivewireless channel between the transmitter and the receiver looksfrequency-flat (see section 3.4.4.3), and therefore advancedfrequency-selective scheduling might not be needed in NX. However, inorder to enable coordination gains and excellent network performancealso at high load, there is still a desire for a network-controlledscheduling design. It is assumed that the network can control the usageof radio resources by means of explicit assignment signaling. Schedulingassignments can be sent on a dedicated control channel or in-band, as aMAC control element, for future sub-frames. Maintaining a flow ofscheduling assignments may be particularly efficient forreciprocity-based Massive MIMO, where control signaling using valid CSIis significantly more efficient than sending control signaling withoutCSI. Both dynamic and semi-persistent allocation of resources ispossible. At least for semi-persistently allocated resources, it ispossible to configure the option of not using the allocated resource ifthere is no data or control signaling to send in the given time-slot.

However, for some situations the latency and/or cost to enableobservability and control from the network do motivate a distributedmeans of control, as well. This is achieved by means of resource controldelegation, the network delegating a part of the radio resources,associated with a set of rules and limitations. Limitations can include,for example, priorities between resources, indication on whether theresources are dedicated or shared, listen-before-talk rules, power orsum-resource usage limitations, beamforming limitations, etc. Thisdesign principle covers D2D (section 3.1.1), contention-based access(section 2.2.6), multi-point connectivity (section 3.12), and otherfeatures where strict network control is infeasible and/or inefficient.

2.2.4.1 Reference Signals

A number of different reference signals are provided in NX, for channelestimation and mobility. Both the presence of the reference signals aswell as the measurement reports are controlled by the scheduler. Thepresence of signals can be dynamically or semi-persistently signaled toone or a group of users.

Also, reference signals for active mode mobility (MRS) can bedynamically scheduled. A UE is then assigned with a search space formobility transmissions. Observe that this search space is potentiallymonitored by one or more UEs and/or transmitted from one or moretransmission points.

Scheduled reference signal transmissions (such as MRS) contain a locallyunique (at least within the search space) measurement identity in thedata message, and reuse some or multiple of the pilots in thetransmission both for demodulation and measurement purposes, implyingthat it is a self-contained message. Further details on referencesignals are given in section 2.3.

2.2.4.2 Link Adaptation

Rate-selection is also performed by the network, to benefit fromcoordination features enabling better prediction of the channel state.Different NX use-cases and scenarios have very different link adaptationinput and requirements. To support uplink link-adaptation, power (orpath-loss) estimates and sounding signals are desirable. For downlinklink-adaptation, both uplink (reciprocity) and downlink pilot-basedestimation are desirable. For downlink pilot based link-adaptation, theCSI concept from LTE with CSI-processes and CSI-RS and CSI-IM (forinterference measurements) may be maintained (see section 3.4). TheCSI-RS transmission and measurements are controlled from the scheduler,in both time and frequency. For most use-cases, the CSI-RS can be keptin-band together with data transmissions, but in some scenarios explicitsignaling of CSI-RS is desirable, e.g., for sharing of CSI-RS resourcesbetween users. CSI-IM and interference reporting is also used, forreciprocity-based beam forming.

2.2.4.3 Buffer Estimation and Reporting

Buffer estimation is used to support uplink scheduling. Datanotification can be done using a data transmission on a pre-assignedresource or using a single (or few) bit indication on an uplink channel.Both of the options can be either contention-based or contention free,e.g., a semi-statically configured contention-based UL channel or adynamically scheduled directly decodable UL channel may be used for thispurpose. An existing data resource can provide a lower latency, whilethe scheduling request bit enables better control of the radio resourcesand potentially better spectral efficiency. A scheduling request channelmay not be needed in NX if the regular uplink channels, potentiallyusing code-division, are sufficient. Scheduling request transmissionswhen the UE is not dynamically scheduled rely on having a pre-configuredgrant; in other words, scheduling requests do not have any specialphysical channel. Normally, scheduling requests are transmittedimplicitly, by means of transmitting pre-defined UL reference signals(such as an RRS), or explicitly, by means of using a pre-granted cPDCHchannel.

2.2.4.4 Multi-Connection Scheduling

Scenarios like multi-hop and multi-connectivity may lead to multiplecontrolling nodes for one served node. Coordination of the controllingnodes is important, where the controlled node can be used for some ofthe decision making, for example for selecting between conflictingassignments or to distribute state information to controlling nodes. Forobservability, the outcome of any distributed decision making may be fedback to the controlling nodes.

The structure described herein, with in-band and in-beam control,significantly simplifies the multi-connectivity use-cases. In scenarioswhere, for example, the downlink data channel is scheduled from one nodeand the uplink data channel is scheduled by another node, additionaluplink and downlink control channels to both nodes are typicallydesirable as well. By ensuring that these control channels are in-band,the maintenance and usage of control channels associated with multiplenodes is simplified.

2.2.4.5 Interference Coordination and CoMP

With a higher usage of directional beamforming, interference is expectedto be bursty to a higher degree. This property provides a largerpotential for coordination gains through coordinating the spatial usageand utilizing the extra degree of freedom for interference control inthe few cases where it is needed.

In NX, interference can come from a large number of different sources,e.g., normal neighbor node signals, pilot pollution in reciprocity basedMIMO, UE2UE and BS2BS interference in dynamic TDD and side-linkcommunication, and other systems in shared spectrum bands.

To support these kinds of features, a set of measurements is desirable.For some features, UE-triggered reports on experienced interference orhigh received power of a given sequence are suitable. In somewell-coordinated scenarios, the use of CSI-reports measured onCSI-RS/-IM is preferable.

2.2.4.6 Group and Dedicated Scheduling

UEs may monitor one or more group-scheduled messages in addition to thededicated messages. This is done by configuring the UE to not onlymonitor DCIs for a UE-specific CRC (typically the UE temporary identityis used to mask the CRC), but also for one or more group CRCs.

One typical use case for this is to enable UEs to measure on dynamicallyscheduled reference signals such as CSI-RS, mobility RS, and beam-RS.FIG. 26 shows an example where UE, is assigned resources containingadditional CSI reference signals, and more generally illustrates anexample of using group scheduling to distribute information aboutdynamically available reference signals (CSI-RS in this example). Thesereference signals may be useful also for other UEs and for that purposea group scheduled message may be transmitted on e.g., the PDCCH toenable non-scheduled UEs to receive and measure on the CSI-RS signals.

2.2.5 Management of Directional Interference 2.2.5.1 Methods forDirectional Interference Management

When there is high-gain beamforming, one or more of three aspects may beconsidered in interference control. The first is that the interferedarea from a narrow TX beam is much smaller than from a wide beam. Thesecond is that high-gain receiver beamforming is strong for rejectinginterference. The third is that the interfered area by a narrow TX beammay have high interference power density. Considering these aspects,there may be two effects: the first is that the number of considerableinterferers for one victim receiver may be very few, most probably onlya single considerable interferer at any given time; the second is thatthe experienced interference of a victim receiver may vary largely andquickly, depending on whether the transmitter of the aggressor link istransmitting or not. The interference control in NX considers the abovecharacteristics:

-   -   The utilization of high-cost interference control method should        be careful. An interference control method at the cost of        considerably reducing radio resource utilization (e.g.,        transmission power, spatial-time-frequency resources) of the        interfering link can be categorized to high-cost interference        control method, for instance, the uniform transmission power        control, reduced power sub-frame or almost blank sub-frame.        Since there is a risk that the benefit by the victim link from        the reduced interference may not be able to compensate the loss        of the interfering link due to the reduction of the radio        resource utilization, such methods shall be cautiously applied,        from the system perspective. However, when there is a risk that        the victim link starves from a long-time strong interference        from the interfering link, some of such methods may be applied,        to ensure the minimum acceptable experience of the victim link.    -   One or more cost-free or light-cost (with no or low radio        resource utilization reduction) interference control methods may        be prioritized:        -   Coordinated link adaptation to protect the TX opportunities            with low interference from the TX opportunities with high            interference according to the interference knowledge based            on DLIM.        -   Coordinated scheduling to avoid the simultaneous scheduling            of the interfering and victim links when there are multiple            candidate links.        -   Coordinated AP selection to change the TX beam direction of            the interfering link or the RX direction of the victim link            to pursue both the load sharing gain and interference            control gain.

2.2.5.2 Aligned Directional Sounding and Sensing (ADSS)

As seen in Section 2.2.5.1, interference awareness is important forinterference control with high-gain beamforming. An Aligned DirectionalSounding and Sensing (ADSS) scheme is developed to derive a DirectionalLink Interference Map (DLIM), where the DLIM is used for interferencecontrol. ADSS is designed to align the interference sounding andmeasurement in the network via a time-frequency pattern defined byDirectional Sounding and Sensing Interval (DSSI) and DirectionalSounding and Sensing Period (DSSP). During the DSSI, each transmittertransmits one link-specific beam-formed sounding signal over theconfigured Sounding Resource Unit (SRU) in its link direction, and eachreceiver keeps a sensing state in its link direction for all possiblesounding signals over all SRUs. Each link receiver reports the measuredresults (periodical or event-triggered), including the interfering linkidentity and the corresponding interference level. Based on thecollected measurement results, the network can derive the DLIM.

FIG. 27 shows a time-frequency pattern for ADSS, showing the ADSSpattern and the dimension of DSSI for ADSS (T for Tx DSSW and R for RxDSSW). The DSSP (the effective time of the DLIM) depends on the variousfactors: the UE moving speed, the beam width of the TX beam, thedeployment and dimension of access nodes. The DSSP may be 203 ms(outdoor) and 389 ms (indoor) and the overall overhead is much less than1%, for example. The ADSS can be either a separate process or a jointedprocess with other channel measurements. The following solution assumesthat the ADSS is a separate process.

Assuming a TDD system, there may be AP-to-AP and UE-to-UE interference,in addition to the AP-to-UE and UE-to-AP interference. One DSSI isdivided into N Directional Sounding and Sensing Windows (DSSW): each APowns one TX DSSW (TDSSW) for sounding signal transmission for the linksplus N−1 RX DSSWs (RDSSW) for sensing of the sounding signal fromneighboring links. Deafness of ADSS is conquered via such dimensioningand the missed interference is avoided.

ADSS may be further developed to reduce overhead so that frequent ADSScan be applied for burst-like traffic, for instance, sharing the sameprocess between ADSS and channel measurement is one way to share theoverhead. The reporting overhead may be reduced as well by well-definedtrigger condition. Decentralized and reactive directional interferencesounding and sensing is also possible. In the event that there is nocentral controller or the interference occurrence is rare, this methodmay be useful.

2.2.5.3 Use Cases

The ADSS is attractive in multiple aspects. A first one is that theaccess link and the self-backhaul link are measured via the sameprocess. The sounding results can be used for the backhaul route(capacity and path) management. A second is that all types ofinterference (AP-to-AP, UE-to-UE, AP-to-UE and UE-to-AP) are measuredvia the same process. There is no need for multiple types of soundingsignals, which is attractive for both TDD and FDD systems, especiallyfor dynamic-TDD system. A third aspect is that via certain alignmentbetween co-existing networks in shared spectrum bands, inter-networkinterference awareness may be achieved via ADSS.

2.2.6 Contention-Based Access

In high-load scenarios, the default transmission modes are based onmaintaining coordination by means of a resource scheduler. However,contention-based access can provide lower delay for initial uplinktransmissions and in relay nodes. This is shown in FIG. 28. As shown atthe top of FIG. 28, scheduled-based access is contention free, and theperformance is superior in high load scenarios. As shown at the bottomof FIG. 28, contention-based access can provide lower delays for initialuplink transmissions and in relay-nodes with a large delay to a centralscheduling unit.

The contention-based uplink channel cPDCH is very different from thenormal contention-free uplink channels dPDCH and rPDCH. A UE needs agrant to transmit on the cPDCH, but it is not forced to use the grant incase it does not have any uplink data to transmit (in the event that theUE has a grant for a dPDCH/rPDCH and it has no data, it should fill thegrant with padding).

When utilizing a cPDCH the UE should include a temporary UE identity(this may be 24 bits long in NX, for example), so that the receivingbase station knows from who the transmission originates. The UE shouldalso add a sequence number to indicate the HARQ buffer that the datacomes from. This is because the grants for the dPDCH/rPDCH transmissionsinclude a HARQ process ID and a new data indicator, which the grant forthe cPDCH does not. An additional difference is that thecontention-based channel cPDCH does not support soft-combining of HARQre-transmissions, something that is supported on the dynamicallyscheduled and contention free rPDCH (see sub-section 2.2.8 for furtherdetails).

Transmissions on the cPDCH may interfere with other channels, primarilysince the UL synchronization in the UE may not be as accurate when thischannel is used. Solutions to this may be implementation-specific. Thescheduler may, for example consider the need for guard bands towardscontention-free channels and ensure that the performance is good enough.Furthermore, since some poorly synchronous UEs will have a random timingoffset, the actual transmission time may have to be significantlysmaller than the uplink resource allocation in some cases. Note thatwhen using massive MIMO beam-forming, there are spatial ways to handlethe interference.

Transmissions on cPDCH may also be restricted by additional access rulessuch as listen-before talk, and this could apply to both shared anddedicated spectrum scenarios. In a dedicated spectrum, for example,dynamically scheduled transmissions (dPDCH/rPDCH) may be to beprioritized. To efficiently enable both transmission principles(scheduled and contention-based access) NX is designed to prioritizescheduled access over contention-based access in a slotted manner byadding a listen-before-talk (LBT) period in the beginning of eachsub-frame. If a specific reference signal, or energy above a threshold,is detected in this period, then the sub-frame is assumed to be occupiedand the contention-based transmission is deferred. The data transmissionfor contention-based access is hence shorter in time, since it initiallyreserves a set of symbols for LBT. For sub-sequent UL transmission,scheduled access is generally better (since it is collision free), andhence NX utilizes contention-based access primarily when the timerequired to maintain coordination increases delay. This is shown in FIG.29, which shows that prioritization between scheduled data andcontention-based data access is enabled by having the scheduled datastarting earlier than contention-based data. This enables thecontention-based access to detect the scheduled data transmission usingcarrier sense. Additional prioritization between differentcontention-based accesses is also possible, by having different lengthof the carrier sense period starting from the beginning of thesub-frame.

To handle “hidden node” situations, e.g., when a mobile terminal with acontention-based grant is unable to detect that there is an ongoinguplink transmission (that the channel is occupied), a clear-to-send(CTS) signal may be added. This is shown in FIG. 30, which illustratescontention-based access with collision avoidance utilizing bothlisten-before-talk (LBT), to prioritize scheduled transmissions, andclear-to-send (CTS), to resolve hidden node problems. Thecontention-based transmission is then divided into two time intervals,where an indication if the second part is allowed to be transmitted isderived by the reception of a CTS signal from the network in the timebetween the two time intervals. The time between the two (transmission)time intervals is referred to as the interruption time.

With contention-based access in dynamic TDD there is thus both aListen-before-talk interval for avoiding collisions with scheduledframes and a CTS-like contention resolution mechanism. NX channels withcontention-based access thus use the following protocol for collisionavoidance:

-   -   Listen for N (one or few) symbols;    -   Transmit one symbol;    -   Listen for contention resolution one/few symbols (<N);    -   Transmit until end of TTI if needed.

The first contention-based transmission may be seen as a schedulingrequest (SR) or a request-to-send (RTS) transmission. Since the mobileterminal may have additional information about the current channel use(e.g., by detecting interference and or PDCCH transmissions from othernodes) one option in NX is to indicate in the RTS signaling whichresources that the mobile terminal would like to utilize. This isdenoted “selective-RTS (S-RTS) and can be further extended with anadjusting-CTS (A-CTS) message from the network. This is shown in FIG.31, which illustrates an example of a proactive RTS/CTS scheme withselective-RTS (a scheduling request containing a physical resourceproposal) and adjusting-CTS (an uplink transmission grant). Userterminals base the S-RTS resource selection on a capability to monitormultiple downlink physical control (PDCCH) channels (configured in the“PDCCH monitor Set” message from the serving node).

Note that the S-RTS may be based on the terminal being reactive orproactive when selecting resources that it wants to use. The selectioncan be based on, e.g., interference measurements (re-active); or controlchannel decoding (pro-active).

The use of an adjusting-CTS message from the network is useful also ine.g., multi-connectivity scenarios, e.g., the network mode may alreadybe using some of the resources selected by the mobile terminal in someother connection.

2.2.7 L2 Multi-Connectivity Mechanism

Multi connectivity is a use-case that puts particular requirements onthe protocol design. It is clear that multiple streams can be maintainedon different layers of the protocol-stack dependent on the ability tocoordinate the buffer handling.

In the simplest case, one base station controls one carrier, but isusing multiple code-words. In this scenario it is natural to domultiplexing between MAC and RLC, e.g., to operate on the samesegmentation/concatenation entity. This may also be the case for fastcoordination between nodes or carriers.

In a slower coordination case it is not possible to fully coordinate thebuilding of the transport blocks. In this case multiplexing needs to bedone before the segmentation entity. In this case flow control isdesirable.

ARQ, where utilized, may be placed before or after the splitting.

Since splitting/merging can be done on different levels, in-orderdelivery, where utilized, operates above the highest split.

2.2.8 Re-Transmission Mechanisms

The current HARQ feedback protocol of LTE relies on fast but error-pronesingle bit feedback with a fixed timing. Since it is far from 100%reliable, the higher layer RLC AM is required to ensure reliability,something which adds delay. Also, the current HARQ protocol is based onmany strict timing relations (such as e.g., as per-HARQ buffersynchronous timing), something which is very inflexible and causesseveral problems when e.g., operating using Dynamic TDD.

For NX, the HARQ protocol should be fast, have low overhead, bereliable, and not require fixed timing. The RLC retransmission protocolis still desirable, to efficiently support multi-hop and mobilityscenarios.

Different L2 protocol architectures result in different design optionsfor L2 functionalities regarding multi-hop communications, such as theARQ or routing.

2.2.8.1 Downlink HARQ/ARQ Design

For NX, a two-layered ARQ structure is kept, as is done with RLC/HARQ inLTE. Differences from LTE are in the HARQ re-transmission layer, whichis fast and low-overhead, but also reliable and not requiring fixedtiming.

For NX, the improved HARQ protocol has one or both of two components:

-   -   A “Super-Fast HARQ” feedback (A), which provides as        fast-as-possible HARQ feedback, albeit not fully reliable.    -   A “Scheduled HARQ” feedback (B), which provides an efficient,        near-100% robust, HARQ feedback suitable for use in e.g.,        Dynamic TDD scenarios.

On top of this, an additional RLC ARQ (C), which is similar to thecurrent LTE RLC AM ARQ, may also be applied.

The detailed ARQ operation depends on the scenario, e.g., either all ora subset of these ARQ components (A, B, C) could be used. Anillustration of the ARQ structure is shown in FIG. 32. Shown in thefigure is an improved ARQ process for single-hop NX. As discussed above,the HARQ protocol illustrated in FIG. 32 utilizes two different feedbackmechanisms: one “Super-Fast” (A) and one “Scheduled” (B). On top ofthis, an RLC layer (C) handles residual errors (e.g., due to mobility)and re-segmentation.

The “Super-Fast HARQ” feedback (A) is designed to be lean and it istransmitted as soon as possible. It provides feedback for one or a fewdownlink transmissions. The feedback contents could be a single bit(ACK/NACK) like in LTE and sent after decoding (or failure to decode)based on received downlink assignment, or the feedback could even besent before complete decoding, e.g., “likelihood of decoding islow/high”. It is further not restricted that the contents should be justone single bit, but it can also be soft quality measure. An example ofusage of “Super-Fast HARQ” feedback is depicted in FIG. 33. In theillustrated examples, the fast HARQ feedback is transmitted at the endof the first available UL transmission occasion. The left side of thefigure shows an FDD or small-cell TDD example where HARQ feedback isincluded in a single OFDM symbol. The right side illustrates an examplewith half-duplex FDD or large cell TDD, where the fast HARQ feedback isincluded in the last OFDM signal of the scheduled uplink transmission.

Upon receiving this “Super-Fast HARQ” feedback (A), the network acts onthe received information by, e.g., either—in case of a (probably)unsuccessful decoding—retransmitting the same data on the same HARQprocess or—in case of a (probably) successful decoding—transmitting newdata on another HARQ process (or possibly the same HARQ process, in caseno new HARQ process is available). The “super-fast HARQ” feedback isassumed to be transmitted on a scheduled dPDCH resource that istypically granted together with the associated DL assignment.

The “Scheduled HARQ” feedback (B), also in this document denoted the“Polled HARQ” feedback, is a multi-bit HARQ feedback scheduled on theuplink data channel, typically the dPDCH. It provides a good, simpledesign preferable for dynamic TDD scenarios, for example, where it isrequired that the protocols can handle dynamic and possibly varyingtiming relations. Being able to convey many bits of information, thisfeedback can be rather extensive, and hence it is good to ensure thatthe base-station beam-former is pointing towards the UE whentransmitting, to ensure as favorable link-budget as possible. It furtherprovides robustness, e.g., by means of being CRC protected and also byincluding built-in error mitigation techniques as described below.

Being a scheduled feedback, the network sends an UCI grant to the UEindicating which, or at least the number of, HARQ processes that shouldbe reported in the feedback. This UCI grant also indicates the explicitresources on which this transmission is to take place—unless of coursethis has already been assigned via RRC, in which case the UCI grant neednot contain such detailed information.

With respect to the report contents, it can be full size, covering allthe allocated HARQ processes for this UE in the downlink direction.Also, a smaller report can be sent, which covers only parts of theallocated HARQ process. Moreover, a differential report can be sentwherein e.g., the status is reported for HARQ processes not having beenreported in the last sent reports. Which of these reporting types areused can be either configured via RRC or explicitly indicated in thereceived UCI grant.

For NX, the “Scheduled/Polled HARQ” feedback (B) may consist of 2 bitsper HARQ process. This HARQ feedback is only transmitted when the UE isscheduled for a normal UL transmission, as shown in FIG. 34, which showsthat Polled HARQ feedback reports are transmitted in the directlydecodable part of normal scheduled uplink transmissions. Note that thedPDCH transport block is protected by a CRC, and hence the likelihood ofreceiving an erroneous polled HARQ feedback report is low. The twofeedback bits per HARQ process are:

-   -   NDI-toggle-bit: Indicates if the feedback relates to an odd or        even packet in the process. This bit toggles each time the UE        receives a new-data-indicator (NDI) in the downlink grant        associated with this HARQ process.    -   ACK/NACK-Bit for the HARQ Process

The maximum number of HARQ processes is configurable between N={1, 2, 4,8, 16, 32, 64}, and hence a full polled HARQ feedback report consists of2N bits. The use of smaller polled HARQ feedback reports, e.g., usingdifferential, compression, or partial reporting schemes, is possible.The polled HARQ feedback report age is configurable (e.g., 1, 2, 3, or 4TTIs old).

2.2.8.2 Uplink HARQ/ARQ Design

For scheduled uplink data transmissions, HARQ feedback is not explicitlycommunicated but is dynamically handled by allocating uplink grants withthe same process ID and a new data indicator (NDI) which is used torequest retransmissions.

In order to support re-segmentation, an additional bit in the DCI can beadded, e.g., a reception status indicator (RSI), to indicate that thegiven data in a HARQ process is not correctly delivered but a newtransport block is requested.

One major error event that can occur for uplink HARQ is false detectionof uplink grants, leading to a UE discarding undelivered data. However,the probability of multiple consecutive false detection events whilehaving data in the uplink buffer is very small, with a reasonable CRCsize and search space.

In case of III bundling or persistent uplink scheduling, the UE alsoincludes the process ID in the uplink transmission in an UCI inside ofthe uplink dPDCH. A special HARQ feedback report (similar to the polledfeedback message used for downlink HARQ) is sent as a MAC controlelement on the downlink dPDCH.

On uplink contention-based channels, soft combining of re-transmissionattempts does not need to be supported, the reason being thatcontention-based channels are easily colliding and then the soft-buffersare likely to be very noisy and it is better to discard the data. In theevent that this assumption is not valid, e.g., when there is a verylarge number of antenna elements, soft combining might be used.

When transmitting on a contention-based resource, the UE should includean additional sequence number, which is encoded as an uplink controlinformation (UCI) element in the uplink dPDCH. ARQ withoutsoft-combining is supported and the ARQ feedback can in that case beprovided in a separate feedback message in a MAC control element.However, typically an uplink contention-based transmission is followedby a DCI containing a grant for a scheduled uplink transmission, whichthen implicitly also contains the ARQ feedback for the contention-basedtransmission.

2.2.8.3 Dynamic Soft HARQ Buffers

The size of the soft buffer is a UE capability for NX. A UE supporting acertain maximum number of HARQ processes is not required to also supportsoft-packet combining when operating at very high data rate. See FIG.35, which shows that the number of HARQ process for which the UE performsoft packet combining may depend on the packet size.

Soft buffers for many 10ths of Gbps can be very large and can thereforebe very expensive. Soft buffers for lower rates are small and cheap incomparison, and thus it can be required of the UEs that they supportsoft combining in those situation. The use of a very large soft bufferin the device should be optional, e.g., as a cost-benefit tradeoff. Thebenefit of improving performance with soft packet combining in difficultscenarios (e.g., low rate cell edge) is significant, while the cost isstill reasonable.

2.2.8.4 Multi-Hop ARQ Protocol Architectures

Sections 2.2.8.1 and 2.2.8.2 described how the desired ARQ protocolarchitecture for NX looks in a single-hop scenario. Now, in amulti-hop/self-backhauled scenario, some additional considerations arerequired.

First of all, the different hops in a multi-hop/self-backhaul chain mayhave very distinct characteristics. They may differ in terms of one ormore of, e.g.:

-   -   Radio Link Conditions/Quality (e.g., SINR, channel properties        etc.)    -   Rx/Tx Capabilities (e.g., number of antennas, max Tx power,        beamforming, receiver procedures, interference suppression        capabilities etc.)    -   Traffic and Routing (e.g., number of multiplexed users, number        of multiplexed routes, amount buffering etc.)    -   (Dynamic) TDD Configuration    -   etc.

Hence, per-hop RRM mechanisms (e.g., link adaptation, segmentation,etc.) are desirable. In particular, a per-hop ARQ mechanism—such asdescribed in the Sections 2.2.8.1 and 2.2.8.2 is still desirable, asfurther discussed in this section.

Secondly, as the number of hops grow, the cumulative probability offailure in the per-hop ARQ mechanism somewhere along themulti-hop/self-backhauled chain increases. Also, cases of classicalmobility (e.g., the UE attaches to another AP/RN—possibly also belongingto another anchor BS/CH) or when the path to the UE is re-routed (e.g.,RNs in the multi-hop/self-backhauled chain is removed/added) needs to beaccounted for. Essentially, in a scenario with mobility and/or not fullyreliable per-hop (H)ARQ, a separate mechanism is used to ensureend-to-end reliability. Put simply, yet another end-to-end ARQ layer isdesirable in these situations, as discussed below.

There are three possible ARQ protocol architectures for themulti-hop/self-backhauled scenarios:

-   -   Alt. 1 “Per hop HARQ/RLC ARQ”: The single-hop ARQ architecture        as described in sections 2.2.8.1 and 2.2.8.2 is utilized over        each hop—inclusive of both HARQ and RLC ARQ.    -   Alt. 2 “End to End RLC ARQ”: Again, the same single-hop ARQ        architecture is utilized over each hop as in Alt. 1 above—but        now with only HARQ and no RLC over each hop. A higher layer RLC        (inclusive of ARQ, segmentation etc.) is instead placed only at        the end-point nodes, e.g., in the BS and the UE.    -   Alt. 3 “Two Layered RLC ARQ”: This is essentially a combination        of the two other ARQ architectures, with a full-blown single-hop        ARQ including HARQ and RLC ARQ for each hop and—in addition—an        extra higher layer RLC is placed on top of this in the end-point        nodes.        The above listed alternatives are depicted in FIG. 36.

Pros and cons of the above listed three possible ARQ protocolarchitectures for multi-hop/self-backhauled communications aresummarized in Table 2 below.

TABLE 2 Alt. 1: Alt. 2: Alt. 3: Two Per hop ARQ End to End ARQ LayeredARQ Pros Low delay, fast. Solve the Cons of Alt. 1 Pros Alt. 1 + Lessfeedback Pros Alt. 2 signaling. Cons Does not handle failure, Lost thePros of Alt. 1 Extra re-routing and mobility If HARQ not 100% overheadfor relay nodes well. reliable, costly due to All UE mobility requiresretransmissions two protocol PDCP retransmissions from endpoint. layers.from endpoint Need to introduce Need to introduce in- segmentationorder-delivery in PDCP. functionality in MAC.

The transmitting RLC entity in one endpoint (e.g., in the BS or UE) ofthe end-to-end RLC layer of Alt. 2 and Alt. 3 above buffers eachtransmitted packet until this is positively acknowledged by thereceiving RLC entity (e.g., in the UE or BS) where after it is removedfrom the buffer. The transmitting RLC entity needs to have its ARQretransmission timer set accordingly depending on the total end-to-enddelay, to the peer RLC entity in the other endpoint, in order not tocause premature retransmissions. An appropriate timer value thereforemay be estimated in various ways, but this procedure may obviously becumbersome in dynamically changing environment and/or complex routingscenarios. In such cases it is better if this timer is disabled andend-point retransmissions are triggered only by explicit negativeacknowledgements from the receiving endpoint RLC entity.

It should be noted, that this end-to-end RLC layer of Alt. 2 and Alt. 3above need not necessarily be a new protocol layer on its own, but couldbe part of the PDCP. In fact, the existing retransmission mechanisms ofPDCP could be used for the purpose of providing this desired end-to-endreliability. This is however a bit problematic with respect to routing,as discussed in Section 2.2.8.5, below.

Summarizing the above, it is clear that it is beneficial to be able toperform retransmissions and segmentation over each hop, which may ruleout Alt. 1 as a suitable candidate—at least in scenarios with mobility,possibly re-routing or with a not fully reliable per-hop (H)ARQmechanism. Further, only relying on end-point retransmissions as in Alt.2 may be inefficient and may require MAC level segmentation (if wantingto support per-hop re-segmentation). Hence also Alt. 2 may be ruled outas a suitable candidate. Hence the Two Layered ARQ of Alt. 3 may be theonly feasible and generic enough architecture to suit the foreseenscenarios.

A Relay ARQ is an improved version of the Two Layered ARQ architectureof Alt. 3 above, which integrates the ARQ of the extra RLC′ layer intothe per-hop relay RLC layer, as shown in FIG. 37.

An aspect of relay ARQ is that the temporary retransmissionresponsibility is delegated from the sender node (the source node or therelay node) step-wise from node to node until finally the data unit isreceived at the receiver. The ultimate retransmission responsibility,however, remains with the source node (BS or UE). This is all the sameas what happens in Alt. 3.

The original assumption for relay ARQ is, however, that each node usesthe same sequence numbering, PDU size and protocol state etc., somethingwhich may not be feasible for dynamically changing channel quality foreach hop. However, some solutions could be adopted to handle thisproblem. By adding a sequence number relation mapping table in the relaynode, the segmentation functionality could still be supported.Alternatively, the existing re-segmentation mechanism of LTE could beused, together with some possible optimizations in order to e.g.,alleviate the overhead caused by multiple step re-segmentations. Forexample, in certain embodiments, only fully assembled RLC SDUs, and notindividual segments thereof, are forwarded on the following link.

Regardless of whether the Two Layered ARQ approach of Alt. 3 or theRelay ARQ architecture is used, it is only in the end-points (e.g., BSand UE) where in-order delivery of RLC SDUs shall be employed, whereasthe intermediate relay nodes (RN) shall deliver the RLC SDUsout-of-sequence. The reason for this is that it is only the higherprotocol layers in the end-points which may require in-order delivery ofdata, whereas requiring in-order delivery in the intermediate nodes mayrisk under-utilizing the links. Also, by not requiring in-order-deliveryin each intermediate node, the data packet may be freely mapped overmultiple-paths, hence achieving a load balancing over intermediate linksand nodes.

2.2.8.5 Routing Consideration in Multi-Hop L2

The design choice for the relaying architecture to support multi-hoprouting in a multi-hop network does impact the ARQ design. As discussedin Section 3.6.6, relaying may be done in on L3/IP or in L2 wherein forLTE relays, for example, the routing is done above PDCP layer. For NX,however, the PDCP layer has its entities only in the anchor nodes, e.g.,BS and UE, but not in the intermediate relay nodes, since otherwise theciphering/security mechanisms of PDCP would require complex handling ofeach such relay node. Hence, the problem is how to perform routing in NXwithout having a PDCP layer in each node.

One option is that each user is handled separately over all hops, e.g.,separate protocol-entities are set up in all nodes along the route andno multiplexing is done between users. This is simple from a protocollayer perspective, but scales poorly with many users and many hops.Also, the L1 procedures are complex, since each relay node needs tomonitor and process data separately for any user routed through thenode.

Another option is that the routing is included in or between one of theL2 protocol layers. The layer where the routing identity is includeddepends on the layer of the multi-hop scheme. This could for example, bedone in the additional RLC′ layer introduced in Section 2.2.8.4 or theTwo Layered ARQ approach (Alt. 3). This layer then contains, apart fromthe regular RLC functionality, also the routing functionality of PDCPbut not the other parts of PDCP, e.g., the ciphering/security. Hence asmall UE context could be desirable in each relay node, in addition towhat was shown in FIG. 36. In the case when Relay ARQ is used, the RLC′could then simply be regarded as the “routing” RLC layer.

FIG. 38 illustrates an overview of a multi-hop architecture overview tosupport relay routing. As shown in the figure, in each relay node, therouting information is based on the PDCP identifier and handled in theRLC′ layer. This is possible because there is a Layer 3 routingmechanism in place, which ensures that there are up-to-date routingtables in each (relay) node.

2.2.9 MAC Design for C-MTC

Low latency and high reliability services are further described inSection 3.1. Here, some additional MAC considerations related to C-MTCare discussed.

2.2.9.1 Dynamic Scheduling for C-MTC

Dynamic scheduling, as in LTE today, is considered as a baseline MACtechnique for C-MTC as well. According to this scheme, the base station(BS) assigns resource blocks to different users in a dynamic fashion(e.g., on a need basis). This requires control signaling in the form ofscheduling requests (SR) and scheduling grants (SG) which also increasesthe overall latency. To meet the latency and reliability requirementsfor the C-MTC applications, the dynamic scheduling implies some changescompared to the LTE standard on the physical layer level, e.g., by IIIshortening, high antenna diversity, etc. FIG. 39 shows a signalingdiagram for dynamic scheduling. In dynamic scheduling, resources areassigned on a need basis and the minimum achievable latency is equal tothree TTIs, assuming zero processing delays.

2.2.9.2 Instant Uplink Access for C-MTC

Instant Uplink Access (IUA) is a form of pre-scheduling to allow thetransmission of data packets without scheduling requests. The resourcesare pre-reserved based on latency requirements, the amount and type oftraffic. The IUA is optimal for periodic traffic where the trafficpattern is pre-known and thus the IUA transmissions can bepre-configured accordingly at MAC level. However, to guarantee thedeterministic latency for sporadic traffic, each device requiresdedicated pre-assigned resources to ensure that emergency messages,whenever they occur, are always transmitted within the requireddeadlines. This means that the resources cannot be used by other devicesalthough their actual utilization by the sporadic data (rare events) isvery low. In order to increase the resource utilization, acontention-based IUA (CB-IUA) can be used. CB-IUA allows the sharing ofthe same resources among two or more devices. Since the use of the sameresources by the two devices may lead to packet collisions, contentionresolution mechanisms become mandatory to achieve the requiredreliability levels within the latency bounds. Collision detection can bedone using the demodulation reference signals (DMRS) to differentiatethe users. After a collision has been detected and the devices/usersinvolved in collision have been identified, the base station canindividually poll the devices to achieve higher reliability.Furthermore, the order in which the base station polls the users can beadjusted according to the application requirements, including trafficneeds and prioritization. The process of contention resolution after acollision is shown in FIG. 40.

Moreover, collision risk in CB-IUA can be minimized by some enhancedfunctionalities such as smart grouping of C-MTC devices. The groupingcan be based on the geographical location, functional behavior, or thetransmission pattern aspect. On-the-fly reconfiguration of groups canalso be performed, once a specified collision threshold is passed.

2.2.9.3 Contention-Based Access Using Listen-Before-Talk for C-MTC

This scheme is based on the well-known listen-before-talk (LBT)principle. To avoid over provisioning of resources for not-so-frequenttraffic in C-MTC use-cases, a contention-based access channel (cPDCH) ismade available. However, the bandwidth of the contention-based resourceis allocated according to the scenario (e.g., number of devices in thenetwork and the generated traffic, etc.), so that the latencyrequirements for C-MTC applications are fulfilled.

Furthermore, a contention-based channel can be exploited by thescheduling request (SR) for the best effort traffic or any othersporadic traffic with large payload size. In case of real-time sporadictraffic with small payload size (e.g., alarms), the sporadic data can betransmitted directly on the contention-based uplink channel, using theLBT principle. Thus for C-MTC applications, the decision whether or notto send real-time data over a contention-based uplink channel is madebased on the size of the data. The amount of bandwidth needed can befixed over time or adaptively adjusted according to the traffic loads,number of nodes and the collision probability.

One advanced alternative is to share the contention-based channelresources with other channels. According to this alternative, allresources are considered as available for contention unless reserved.The base station, as a central controller, manages all the resources andalways makes sure of the availability of resources for contention. Theadvantage of this improvement is to reduce the probability of collisionsamong packets by increasing the number of contention channels available.However, it requires additional resource management overhead tocoordinate the resource utilization among the devices based on thepriority levels. Moreover, each device maintains the resource allocationtable that reflects the resources available for contention.

2.2.9.4 Polling Mechanisms for C-MTC

The resource allocation for C-MTC can be enhanced by using thewell-known polling mechanism. According to this scheme, a base stationpolls the devices and adjusts the frequency of the polling based on theapplication requirements, the number of devices, priority levels and thedata generation rate. Polling increases the required control overhead ascompared to IUA where the resources are pre-configured once for severaltransmissions.

One further enhancement of this scheme is the group polling where thebase station polls simultaneously a group of devices. The number ofdevices in one particular group depends upon the availability ofresources, the number of total devices, the latency and the trafficrequirements. There exist two alternatives for resource allocation ingroup polling, as shown in FIG. 41, which shows group polling usingcontention-free (left) and contention-based access (right) techniques.According to these alternatives, the devices polled as a group couldeither contend for the shared resource or use the dedicated resources.The main advantage of using polling mechanisms lie in theirdeterministic nature. It also avoids over-provisioning of resources asin case of IUA. On the other hand, polling mechanisms require additioncontrol signaling in the form of ‘polls’.

2.2.10 Example Use-Cases

For the purpose of explaining how different aspects for the NX L2solution described in this sub-section work together, additionalexamples are provided here.

2.2.10.1 Multi-User MIMO Examples

FIGS. 42 and 43 depict two different examples of MU-MIMO schedulingusing out-band and in-band DCI, respectively. In the out-band (andout-of-band) example of FIG. 42, all DCIs are transmitted on the PDCCH.Since the PDCCH needs to carry a relatively large number of bits itneeds more resources. The UEs need to perform more blind decodingattempts since more UEs are multiplexed on the PDCCH. Since the PDCCHtypically needs to use full power, the PDCH resources overlapping withthe PDCCH resources cannot be used. The delivery of the DCIs isexpensive compared to the data, since no UE optimized beam-forming isused in this example.

FIG. 43 shows an example of MU-MIMO scheduling using in-band and in-beamDCI on directly decodable physical data channel (dPDCH). When DCIs areinstead transmitted in-beam and in-band, as in FIG. 43, on the scheduledresources, the PDCCH resource can be made much smaller. This also leavesmore resources available for the PDCH. The DCI is transmitted on adynamically extended search space inside of the scheduled data channel.Both the directly decodable and the re-transmittable physical datachannels (dPDCH and rPDCH) use the same demodulation reference signalsthat are beam-formed towards each individual UE. The control informationdelivery is cheaper since it benefits from the antenna array gain. Alsothe UE search space can be made smaller since there is no need tosupport user multiplexing on the dedicated dPDCH control channel.

2.2.10.2 Reciprocity Use Case Example

Support for reciprocal massive MIMO and dynamic TDD operation is animportant aspect of NX. This use case is the basis for the examplesprovided below.

Starting with an example with downlink data transfer supportingreciprocal massive MIMO beamforming, as shown in FIG. 44, the servingnode uses the PDCCH to schedule a transmission of reciprocal referencesignals (RRS) from the mobile terminal. Furthermore, the PDCCH containsa DCI with a dynamic search space extension. The RRS transmission needsto cover the bandwidth of the downlink PDCH transmission, to enablebeamforming based on channel reciprocity.

In response to the RRS transmission, the base station transmits thePDCH, comprising a direct (dPDCH) and a re-transmittable part (rPDCH).The mobile terminal finds a DCI in the dPDCH that indicates the formatof the transmission and that also contains a grant for transmitting aresponse.

The first response for the uplink comprises a new RRS and a fastACK/NACK feedback. Since the RRS needs to cover the bandwidth of thedownlink channel, the cost of including additional information in adPDCH is in many cases negligible. The first response typicallytherefore comprises additional feedback such as CSI-feedback,MRS-measurements, and/or rich HARQ feedback information.

For the second DL transmission, the UE is already configured to searchfor the DCI in the dPDCH and no explicit message is required to enablethe UE to search there. The second feedback transmission in this examplealso comprises higher layer feedback (TCP feedback and/or RLC feedback).This is transmitted as uplink data in an rPDCH field. In addition to thefast ACK/NACK, the dPDCH may also contain a larger HARQ feedback report(denoted polled ACK/NACK in the example) as well as additional feedback(CSI, BSR, etc).

Note that in the downlink the dPDCH is placed in the beginning of thetransmission while in the uplink the dPDCH is placed at the end of thetransmission. This is to enable the UE to process and generate thefeedback that it puts in the uplink dPDCH.

FIG. 45 shows a corresponding uplink data transmission example, forreciprocal massive MIMO beamforming. In this example, the UE is firstconfigured with a small RRS and an associated dynamic search space for adownlink dPDCH. When the UE has data to transmit it sends an RRS on thepre-granted resource. This RRS implicitly serves as a scheduling requestand it also enables the base station to send the first downlink dPDCHusing reciprocal based beamforming. The granted uplink transmissionscomprises an RRS (used also for uplink channel demodulation), are-transmittable PDCH, and a direct PDCH at the end. The downlinktransmissions comprises a direct PDCH containing UL grants (withimplicit HARQ feedback) and additional request for feedback to betransmitted by the UE. The downlink transmissions also comprise are-transmittable PDCH containing primarily higher layer feedback.

2.3 Radio Interface Physical Layer 2.3.1 Modulation Scheme

Section summary: NX uses OFDM as modulation scheme in UL and DL,possibly also including a low-PAPR mode (e.g., DFTS-OFDM) forenergy-efficient low-PAPR operation and Filtered/Windowed OFDM forfrequency-domain mixing of numerologies. Note that a “numerology,” asthat term is used herein, refers to a particular combination of OFDMsubcarrier bandwidth, cyclic prefix length, and subframe length. Theterm subcarrier bandwidth, which refers to the bandwidth occupied by asingle subcarrier, is directly related to, and is sometimes usedinterchangeably, with subcarrier spacing.

The modulation scheme of NX is cyclic-prefix OFDM, both for UL and DL,which enables a more symmetric link design. Given the large operatingrange of NX, sub-1 GHz to 100 GHz, multiple numerologies may besupported for the different frequency regions, see Section 2.3.2.3. OFDMis a good choice for NX, since it combines very favorably withmulti-antenna schemes, another significant component in NX. In OFDM,each symbol block is very well localized in time, which makes OFDM alsovery attractive for short transmission bursts, important for various MTCapplications. OFDM does not provide as good isolation betweensubcarriers as some filter-bank based schemes do; however, windowing orsub band filtering provide sufficient isolation between sub bands (e.g.,not individual subcarriers but collections of subcarriers), whereneeded.

Section 2.3.3 outlines that for some use-cases, mixing of different OFDMnumerologies is beneficial. Mixing of OFDM numerologies can either bedone in time-domain or frequency domain. Section 2.3.3 shows that formixing of MBB data and extremely latency-critical MTC data on the samecarrier, frequency-domain mixing of OFDM numerologies is beneficial.Frequency-domain mixing can be implemented using Filtered/Windowed OFDM.FIG. 46a shows a block diagram of Filtered/Windowed OFDM. In thisexample, the upper branch uses narrow (16.875 kHz) subcarriers 400-1100.The lower branch uses wide (67.5 kHz) subcarriers 280-410 whichcorrespond to narrow subcarriers 1120-1640. FIG. 46b shows the mappingof upper and lower branches to the time-frequency plane. During the timeduration of the large IFFT (2048 samples), four small IFFTs (512samples) are performed.

In Filtered OFDM, sub bands are filtered to reduce interference towardsother sub bands. In Windowed OFDM beginning and end of OFDM symbols aremultiplied with a smooth time-domain window (regular OFDM uses arectangular window spanning the length of an OFDM symbol includingcyclic prefix) reducing discontinuities at symbol transitions and thusimprove spectrum roll off. This is shown in FIG. 47, which illustrateshow the beginning and end of an OFDM symbol are multiplied by a smoothtime-domain window.

In the example frequency-domain mixing of OFDM numerologies shown inFIG. 46, the lower branch uses numerology with four times as widesubcarriers as the upper branch, e.g., 16.875 kHz and 67.5 kHz for theupper and lower branch, respectively (see Section 2.3.2.3 for thesupported numerologies). In this example, both branches use the sameclock rate after IFFT processing and can directly be added. However, ina practical realization this may not be the case; especially if one ofthe numerologies spans a much narrower bandwidth than the otherprocessing at a lower sampling rate is preferable.

While filtered OFDM is possible, windowed OFDM is preferred due to itsgreater flexibility.

Sub band filtering or windowing (both at the transmitter and thereceiver) and guard bands are desirable to suppress inter-subcarrierinterference, since subcarriers of different numerologies are notorthogonal to each other. In addition to sub band filtering orwindowing, filtering across the transmission bandwidth is alsodesirable, to fulfill the desired out-of-band emission requirements. Aguard band of 12 narrowband subcarriers enables an SNR of 20+ dB on allsubcarriers, while a guard band of 72 narrowband subcarriers allows anSNR of 35+ dB on all subcarriers. To avoid unnecessary guard bandlosses, Filtered/Windowed OFDM may be limited to two contiguous blocksof different numerologies. To the extent that Filtered/Windowed OFDM issupported by the NX standard, every NX device—even a device onlysupporting a single numerology—should support transmit and receivefiltering/windowing since it could operate on an NX carrier operatingwith mixed numerologies (given the low complexity of windowing it isreasonable to assume that every UE can implement windowing). A networknode on the other hand, needs only to support Filtered/Windowed OFDM ifit supports use case mixes requiring frequency-domain mixing ofnumerologies. Note that detailed specifications of the windowing or subband filtering are not needed, but rather performance requirements totest the chosen implementation. Sub band filtering and windowing canalso be mixed on transmitter and receiver.

OFDM may also include a low-PAPR mode such as DFTS-OFDM. OFDM is used tomaximize performance while the low-PAPR mode might be used in noderealizations (both eNB and UE) where low peak to average power ratio(PAPR) of the waveform is important from a hardware perspective, e.g.,at very high frequencies.

2.3.2 Frame Structure and Numerology

Section summary: At the physical layer, the minimum transmission unit isa subframe. Longer transmissions can be realized by subframeaggregation. This concept enables a variable III, for a giventransmission the III corresponds to the length of the subframe or to thelength of the subframe aggregate in case of subframe aggregation.

Three subcarrier bandwidths are defined to cover the operating rangefrom below 1 GHz to 100 GHz and the large use case space.

NX supports both FDD and dynamic TDD. Even though not relevant for thefirst releases of NX, the concept is extendable to full duplex,especially at the base station, as full duplex technology becomes moremature.

2.3.2.1 Frame Structure

The NX physical layer as described herein has no frames but onlysubframes. It is possible that the concept of frames can be introducedlater. Two basic subframe types, one for UL and one for DL, are defined.These subframe types are identical for both FDD and TDD. FIG. 48 depictsthe basic subframe types, where T_(sf) is the subframe duration. T_(DL)and T_(UL) are the active transmission durations in DL and UL,respectively. A subframe consists of N_(symb) OFDM symbols (see Table3), but not all symbols in a subframe are always used for activetransmission. Transmission in a DL subframe starts at the beginning ofthe subframe and can extend from 0 up to at most N_(symb) OFDM symbols(later start of a transmission in a DL subframe for listen-before-talkoperation is also possible). Transmission in an UL subframe stops at theend of the subframe and can extend from 0 up to at most N_(symb) OFDMsymbols. The gaps—if present—are used in TDD for transmission in thereverse direction within a subframe, as explained below.

FIG. 49 shows how these two subframe types together build up the framestructure for FDD and TDD. FIG. 49a shows the frame structure for TDD.In subframes with UL transmission in the end the DL transmission stopsearly. FIG. 49b shows the frame structure for TDD, UL transmission,while FIG. 49c shows the frame structure for FDD. T_(A) is the timingadvance value by which amount the UL transmission precedes the DLtransmission. T_(GP,DU) and T_(GP,UD) are guard periods required forDL→UL and UL→DL switching in TDD, respectively. It is important to notethat both DL and UL subframes exist simultaneously—during every subframeduration T_(sf) both a DL and an UL subframe exist, even though notransmission may occur in a duplex direction (to avoid simultaneoustransmission and reception in TDD and half-duplex transceivers). Withthis definition, UL transmissions only occur in UL subframes and DLtransmissions only in DL subframes. This simplifies specification, sinceone subframe is then only transmitted from one node

As shown in FIG. 49a , the frame structure also allows for an ULtransmission at the end of a DL-heavy subframe duration by stopping theDL transmission early, as explained previously. As a minimum, the DLtransmission must stop two OFDM symbols before the subframe ends toaccommodate required guard periods for the duplex switch and the ULtransmission itself. This UL transmission can be used for Fast ACK/NACKfeedback but also for other UL information, such as CQI, RRS, and smallamount of user data. In FDD, e.g., as shown in FIG. 49c , the FastACK/NACK is sent at the end of the next UL subframe to allow full usageof the DL subframe and to maintain a common structure with TDD. Even forTDD the processing time to decode and prepare an ACK/NACK is very short,so even here transmission of the Fast ACK/NACK in the next UL subframeis supported. If ACK/NACK decisions can be based on received referencesignals which are transmitted early in the DL subframe, Fast ACK/NACKfeedback at the end of the current UL subframe is even possible for FDD.Note that NX in addition to Fast ACK/NACK also provides a scheduledACK/NACK mechanism to acknowledge multiple transmissions; see Section2.2.8.1.

FIG. 49b shows (for TDD) a subframe duration only containing UL. Therequired guard period is generated by leaving the beginning of the ULsubframe empty.

FIG. 49 also shows the earliest possible re-transmission timing. ForTDD, in principle, it might be possible to schedule a re-transmissionalready in the next DL subframe. However, given realistic decodingdelays at an eNB this is infeasible; the earliest practicalre-transmission possibility is therefore in the next-next DL subframe.It is important to point out that, for NX in both DL and UL direction,an asynchronous hybrid-ARQ protocol is used, where re-transmissions arescheduled at an arbitrary time, with the next-next DL subframe being theearliest possible re-transmission time. For FDD, the earliestre-transmission possibility is one subframe later than in TDD, due tothe delayed ACK/NACK. To match the re-transmission delay of TDD, anextra-large timing advance can be used, which would give the eNB enoughtime to schedule a re-transmission in the next-next DL subframe.

The example in FIG. 49a shows a DL transmission followed by an ULtransmission for, e.g., Fast ACK/NACK. However, the same principalstructure even applies if the beginning of a subframe duration is usedfor DL control and the remaining part for guard and UL. The DL controlin the beginning could for example contain an UL grant; however, in mostcases the UL grant would be valid for the next UL subframe. If the grantwould be valid for the current UL subframe this would imply extremelyshort preparation time at the UE, and in case of FDD also a resourcewaste, since the beginning of the UL subframe would be empty. See FIG.50 for an example. As shown in FIG. 50, an UL grant transmitted at thebeginning of a DL subframe is typically valid for the next UL subframe.If the grant would be valid for the current UL subframe, the beginningof the UL subframe is empty. For extremely delay critical applicationssuch as certain C-MTC use cases, grant validity for the same UL subframecan be considered.

The duration of a single subframe is very short. Depending on thenumerology, the duration may be a few hundred μs or even less than 100μs, in the extreme case even less than 10 μs; see Section 2.3.2.2 formore details. Very short subframes are important for C-MTC devicesrequiring short latency, and such devices typically check for controlsignaling transmitted at the beginning of every DL subframe. Given thelatency critical nature, the transmission itself can also be very short,e.g., a single subframe.

For MBB devices, extremely short subframes are typically not needed. Itis therefore possible to aggregate multiple subframes and schedule thesubframe aggregate using a single control channel. See FIGS. 49b and 49cand FIG. 50 for examples. Subframe aggregation is supported in the DLand in the UL; due to full duplex limitations UL and DL subframe(aggregates) cannot overlap. A single transport block (ignoring MIMO andthe possibility of having two transport blocks mapped to dPDCH andrPDCH; see Section 2.2.2.1) is mapped to a subframe aggregate andacknowledgement of correct reception is done for the subframe aggregateand not individual subframes. This also reduces overhead if FastACK/NACK is used especially for TDD since now a Fast ACK/NACKtransmission (plus guard period) only occurs once per subframe aggregateand not once per subframe.

Multiplexing of individual subframes and subframe aggregation issupported. In DL, when individual subframes overlap with subframeaggregates and the UEs receiving individual subframes should acknowledgethem using Fast ACK/NACK, the aggregated subframe should containtransmission holes to enable UL reception at the eNB.

2.3.2.2 Multiplexing of Data and Control

When present, the Physical Downlink Control Channel (PDCCH) starts inthe beginning of a DL subframe (later start of a transmission in a DLsubframe for listen-before-talk operation is possible; for more detailson listen-before-talk see Section 3.8.4). PDCCH spans preferably 1 OFDMsymbol in time but can extend up to N_(symb) symbols (i.e., up to onesubframe). PDCCH can schedule Physical data channel (PDCH) in the sameand next subframe for DL and PDCH in next subframe for UL. PDCCH may ormay not be able to schedule the UL of the same subframe.

PDCH can span multiple DL subframes. It may start late in a DL subframeif time multiplexed with PDCCH, otherwise it starts in the beginning ofa DL subframe. For TDD, it may end before the end of a DL subframe, toenable UL transmissions at the end of the subframe.

FIG. 51 illustrates examples of data and control multiplexing fordownlink in 67.5 kHz numerology. The configuration on the bottom rightis not supported.

PDCH and PDCCH may occupy different parts of the band and thus need tobe self—with respect to reference signals. See FIG. 52, which shows anexample of mapping control and data to the physical resource. Amechanism for how to handle control channel resources for a given useroverlapping with data resources for another user is desirable. Even ifPDCCH and scheduled PDCH in DL would always overlap in frequency-domain,PDCCH overlapping other users DL PDCH may occur for UL grants.

For uplink and TDD, a PDCH transmission may start late in an UL subframeto create a guard period for DL-UL switch; in FDD a PDCH transmissionsstarts at the beginning of an UL subframe. A transmission ends at theend of an UL subframe. Uplink control information is transmitted in thelast OFDM symbol(s) of an UL subframe, either on dPDCH (see Section2.2.2.1) and/or PUCCH. Frequency multiplexing of control and data ispossible.

2.3.2.3 Numerology

It is well known that robustness of an OFDM system towards phase noiseand Doppler shift increases with subcarrier bandwidth. However, widersubcarriers imply shorter symbol durations which—together with aconstant cyclic prefix length per symbol—result in higher overhead. Thecyclic prefix should match the delay spread and is thus given by thedeployment. The required cyclic prefix (in μs) is independent of thesubcarrier bandwidth. The “ideal” subcarrier bandwidth keeps the cyclicprefix overhead as low as possible but is wide enough to providesufficient robustness towards Doppler and phase noise. Since the effectof both Doppler and phase noise increase with carrier frequency therequired subcarrier bandwidth in an OFDM system increases with highercarrier frequency.

Considering the wide operating range of below 1 GHz to 100 GHz it isimpossible to use the same subcarrier bandwidth for the completefrequency range and keep a reasonable overhead. Instead, threesubcarrier bandwidths span the carrier frequency range from below 1 to100 GHz.

To enable subframe durations of a few 100 μs using LTE numerology (forLTE frequencies), one subframe would have to be defined as a few OFDMsymbols. However, in LTE, OFDM symbol durations including cyclic prefixvary (the first OFDM symbol in a slot has a slightly larger cyclicprefix) which would lead to varying subframe durations. (Varyingsubframe durations are in practice likely not a significant problem andcould be handled. In LTE, the varying cyclic prefix length leads tosomewhat more complicated frequency error estimators.) Alternatively, asubframe could be defined as an LTE slot, leading to subframe durationsof 500 μs. This, however is considered too long.

Therefore, even for LTE frequencies a new numerology is describedherein. The numerology is close to the LTE numerology, to enable thesame deployments as LTE, but provides subframes of 250 μs. Thesubcarrier bandwidth is 16.875 kHz. Based on this subcarrier bandwidthseveral other numerologies are derived: 67.5 kHz for around 6 to 30/40GHz or dense deployments (even at lower frequencies) and 540 kHz for thevery high frequencies. Table 3 lists the most important parameters ofthese numerologies, e.g., f_(s): Clock frequency, N_(symb): OFDM symbolsper subframe, N_(sf): samples per subframe, N_(ofdm): FFT size, N_(cp):cyclic prefix length in samples, T_(sf): subframe duration, T_(ofdm):OFDM symbol duration (excluding cyclic prefix), and T_(cp): cyclicprefix duration). Table 3 is based on an FFT size of 4096 and a clockfrequency of 34.56 MHz to allow the covering of large carrierbandwidths. The proposed numerologies are not based on the LTE clockfrequency (30.72 MHz) but on 16.875/15.30.72 MHz=9/8.30.72 MHz=9.3.84MHz=34.56 MHz. This new clock relates via a (fractional) integerrelation to both LTE and WCDMA clocks and can thus be derived from them.

TABLE 3 Sub- 16.875 16.875 67.5 67.5 540 carrier kHz, kHz, kHz, kHz,kHz, band- normal long normal long normal width CP CP CP CP b CP Main<~6 <~6 GHz ~6 to 30-40 Low delay in >30-40 scenario GHz SFN GHz orwide-area GHz transm. dense depl. deployments f_(s) in 69.12 = 2 × 34.56276.48 = 2 × 138.24 2212 = MHz 2 × 1105.92 N_(symb) 4 3 4 7 4 (largernumber is possible) N_(sf) 17280 17280 17280 34560 17280 N_(ofdm) 40964096 4096 4096 4096 N_(cp) 224 1664 224 4 × 848, 3 × 832 224 CP 5.5 40.65.5 20.5 5.5 overhead in % T_(sf) in μs 250 250 62.5 125 7.81 T_(ofdm)59.26 59.26 14.82 14.82 1.85 in μs T_(cp) in μs 3.24 24.07 0.81 3.010.10 T_(ofdm) + 62.5 83.33 15.625 17.86 1.95 T_(cp) in μs Max 60 60 250250 2000 carrier band- width in MHz

Note that numerologies for implementations may vary from those listed inTable 3. In particular, numerologies with long cyclic prefixes may beadjusted.

FIG. 53 illustrates several example numerologies.

Table 3 shows that OFDM symbol duration and subframe duration decreasewith subcarrier bandwidth, making numerologies with wider subcarrierssuitable for low-latency application. The cyclic prefix length alsodecreases with subcarrier bandwidth, limiting the wider subcarrierconfigurations to dense deployments. This can be compensated by longcyclic prefix configuration, at the price of increased overhead. Inother words, shorter subframes and thus latencies are more efficientlyavailable in small cells than in large cells. In practice, however, itis expected that many latency critical applications deployed in the widearea (and thus require a cyclic prefix larger than 1 μs) don't requiresubframe durations smaller than 250 μs. In the rare cases where widearea deployments require smaller subframe durations, 67.5 kHz subcarrierbandwidth—with long cyclic prefix if needed—can be used. The 540 kHznumerology provides even shorter subframes.

The maximum channel bandwidths of the different numerologies are,approximately, 60 MHz, 240 MHz, and 2 GHz for 16.875 kHz, 67.5 kHz, and540 kHz numerology, respectively (assuming an FFT size of 4096). Widerbandwidths can be achieved with carrier aggregation.

Section 2.3.1 describes mixing of different numerologies on the samecarrier, using Filtered/Windowed OFDM. One of the motivations is toachieve lower latency on a part of the carrier. Mixing of numerologieson a TDD carrier should obey the half-duplex nature of TDD—simultaneoustransmission and reception capability of a transceiver cannot beassumed. The most frequent duplex switching in TDD is thus limited bythe “slowest” numerology among the simultaneously used ones. Onepossibility is to enable duplex switching on the “fastest” numerologysubframe basis when needed and accept losing currently ongoingtransmission in the reverse link.

2.3.3 Physical Channels, Downlink

Section summary: The physical anchor channel (PACH) is used for AITdistribution. The PACH design supports blind detection of usednumerologies. PACH supports beamforming and/or repetition to improvelink budget.

The physical downlink control channel (PDCCH) schedules physical datachannel (PDCH). PDCCH spans only a fraction of the system bandwidth andhas its own demodulation reference signals enabling user-specificbeamforming.

TABLE 4 Physical channels in NX Channel Purpose Physical anchor channelDistributes AIT (PACH) Physical downlink control Schedules PDCH and cantrigger reference channel (PDCCH) signal transmissions and CQI reports

2.3.3.1 Physical Anchor Channel (PACH)

AIT can be distributed via PDCH or via PACH, depending on the UE state.See FIG. 54, which shows AIT mapping to physical channels. The CommonAIT (C-AIT) is periodically broadcasted in PACH as introduced in Section2.2.2.2. In this section, the transmission signal processing,transmission format, and possible blind detection of PACH are described.In Section 3.2, different deployments of how to distribute C-AIT arediscussed. Since UEs are not aware of the deployment, the PACH designshould work in all possible configurations. An overview of the PACHtransmit processing procedure is shown in FIG. 55. Flexible payloadsizes are supported; padding is used to match the payload size includingCRC to one out of {200, 300, 400} bits. If required, this set can beextended. Simulations with these payload sizes show that Turbo coding isbetter than convolutional coding as the channel coding. However, thespecific coding design for PACH may be considered in conjunction withthe coding used for MBB, to harmonize coding schemes.

The encoded data are mapped to QPSK symbols and DFT-precoded to achievea low-PAPR waveform. The precoded signal is mapped to a predefined groupof subcarriers. Broadcast/wide beams are preferred for transmission.However, in some scenarios omni-directional transmission does notprovide the required coverage and beam-sweeping in time domain should besupported, which would be transparent for the terminals.

Different transmission formats (different number of subframes) aredefined to accommodate the different payload sizes. The basic PACHtransmission block for a given payload consists of N_(sf) ^(PACH)contiguous subframes and N_(sc) ^(PACH) contiguous subcarriers. To besimilar to the LTE PBCH bandwidth (1.08 MHz), if the numerology of16.875 kHz subcarrier spacing is deployed, N_(sc) ^(PACH)=72, 1.215 MHz,is selected here. If this bandwidth is too large and cannot betransmitted within a 1.4 MHz channel bandwidth, a smaller N_(sc) ^(PACH)can be selected.

To support flexible payload sizes without additional signaling, N_(sf)^(PACH) is implicitly configured according to a pre-defined mappingtable. The UE blindly detects the transmission format (number ofsubframes N_(sf) ^(PACH)) and derives the payload size from the detectednumber of subframes. Three different formats—one for each payload sizeillustrated above—are defined, consisting of 4, 6, and 8 subframes.Reference signals, each as a pre-defined sequence, are inserted into the1^(st) OFDM symbol in each subframe-pair, e.g., {1^(st), 3^(rd)},{1^(st), 3^(rd), 5^(th)} and {1^(st), 3^(rd), 5^(th), 7^(th)} subframesfor the formats containing 4, 6, and 8 subframes, respectively. A PACHresource mapping scheme with four subframes is illustrated in FIG. 56.UEs can blindly detect the reference signal pattern and derive thetransmission format and payload size.

To support multiple analog beams, a fixed absolute time duration, e.g.,10 ms, is reserved to sweep beams. Note that for TDD, the transmittingnode cannot receive any UL transmissions during this time duration.Thus, a more flexible scheme may be used for TDD. The maximum number ofsupported beams depends on the used transmission format and numerology,since both parameters determine the duration of the basic PACHtransmission block. The basic PACH transmit block can also be repeatedwithin a beam in the duration to obtain the repetition gain, besides ofthe beamforming gain of each block.

The resource mapping schemes are designed to fit with the numerologiesin Section 2.3.2.3. The current design is to guarantee the coding rateof each numerology is about 0.1, similar to the value of LTE PBCHwithout block repetition.

Since the UE may not have a-priori information about which numerology isused for PACH transmission, it needs to detect the numerology blindly.To minimize the complexity, the number of possible numerologies shouldbe small, e.g., coupled to the frequency band. For the lower part of the1-100 GHz range both 16.875 kHz and 67.5 kHz numerologies are relevantand can be used for AIT distribution. For the mid-range and high-rangeof 1-100 GHz, 67.5 kHz and 540 kHz are the preferred numerologies,respectively. Several numerologies support normal and extended cyclicprefix. The PACH design enables blind detection of cyclic prefix length,though the long cyclic prefix could be preferred in some cases, e.g., ifsingle-frequency network (SFN) is used for AIT distribution.

Coupling the AIT numerology for each frequency band to only onecandidate—such that for a given frequency always the same numerology isused for AIT transmission—provides benefits with respect to blinddecoding, but on the other hand forces support of carriers with mixednumerologies (one numerology for AIT and one numerology used for theother transmissions on the carrier) with large design impacts, and istherefore possible but not preferable.

2.3.3.2 Physical Downlink Control Channel (PDCCH)

The physical downlink control channel (PDCCH) carries downlink controlinformation, DCI. DCI includes, but is not limited to, schedulinginformation for PDCH, both uplink and downlink. A PDCCH also containsreference signals for demodulation, the user identity (either explicitlyor implicitly, e.g., CRC mask) and CRC for validation.

FIG. 57 shows Examples of minimum PDCCH allocation unit (CCE) and theirmaximum DCI payload sizes (excluding a 16-bit CRC) when 16-QAM is used.RS are put in frequency-clusters to facilitate antenna portde-spreading.

PDCCH is transmitted preferably in the first OFDM symbol in an NX DLsubframe, a multi-symbol PDCCH can be envisioned if desirable from acapacity and/or coverage viewpoint. A PDCCH is transmitted in a part ofthe spectrum. The size of this part depends on the channel conditionsand payload size. Multiple PDCCHs may be transmitted, frequencymultiplexed or/and space-multiplexed in the same OFDM symbol.Space/frequency resources unused for PDCCH transmission may be used forPDCH transmission.

Payload Sizes

PDCCH is preferably defined for a small number of message sizes to limitthe blind decoding complexity. If a larger set of payload sizes would bedesirable, it is possible that additional message sizes are defined orthat padding to the next larger PDCCH message size is used.

QPSK and even 16-QAM modulation are foreseen as the modulation formatsfor PDCCH. Time/frequency resources are allocated in Control channelelement (CCE) units. The CCE size is connected to the message sizes. TheCCE size should be such that the maximum code rate is 4/5 for thehighest modulation index. In case of 16-QAM, 40 bits, this translates toceil(5*40/4/4)=13 RE. Alternatively, a fixed CCE size may be set to,e.g., 18 RE, which translates to a message size=floor(18*4*4/5)=56 bits,including CRC.

Resources belonging to a single CCE are kept as a contiguous, localized,set of subcarriers, including demodulation reference signals. Aggregatesof CCEs are used to improve coverage, and/or carry large payloads. Theterm “aggregation level” refers to the number of CCEs allocated to onePDCCH. The aggregation level is expected to be powers of two, from oneup to 32. CCE aggregates are contiguous in frequency, i.e., localized.

PDCCH is channel coded using the LTE convolutional code. After channelcoding, the data is scrambled, using a similar scrambling sequence asfor ePDCCH in LTE.

PDCCH contain the CRC of the message body, scrambled by a UE-specificidentity. The UE detects a PDCCH if the descrambled CRC of a decodedmessage matches.

The DCI in LTE has a CRC-16 attached (CCITT-16). The CRC misseddetection probability of not detecting an error in, e.g., an 48-bit DCIcan be upper bounded at 4.3e-4. With respect to C-MTC requirements onthe missed detection probability, it can be observed that given that theBLER operating point is so low and that C-MTC is assumed to make hardlyany use of retransmissions, where the missed detection would lead to aresidual block error, a missed detection probability of 4.3e-4 appearsacceptable.

The false alarm probability for detecting a matching CRC on one searchspace position where no DCI has been transmitted, but the UE is justreceiving noise, can be well approximated by P_(false)=2⁻¹⁶=1.5E−5 for aCRC-16. For N search space positions, the probability increases on firstorder by factor N, for small P_(false). The possible effects of falsealarms are different for DL-grants and UL-grants. In the worst case,where the UE stops searching after the first CRC match, the false alarmprobability from random noise can lead to equally large BLEP, which forCRC-16 is with 1.5E-5 far higher than the extreme C-MTC target of 1 E-9.For CRC-24, the false alarm probability is with 6E-8 still too high. Inorder to reach BLEP<1E-9, CRC-30 is required. CRC-32 would allow for 4search space positions at BLEP<1E-9.

Furthermore, the false alarm probability for detecting a matching CRC ona DCI with a CRC XORed with another RNTI needs to be considered. ThisP_(false). depends on the number of used RNTIs and transmitted DCIs in asubframe.

In each subframe, the BS can address a certain UE through a pre-definedset of possible PDCCHs. Each possible PDCCH is called a candidate, andthe set (with size) is called a search space. The UE evaluates allcandidates in a subframe, delivering validated candidates to higherprotocol layers. The search space is limited by limiting the number ofpossible payload sizes, aggregation levels, and frequency allocations

All PDCCH candidates in a search space hop in frequency betweensub-frames. The hopping is controlled by a pseudo-random sequence.

The default PDCCH search space is transmitted in the carrier'sfundamental numerology. It may be transmitted with beamforming, but istypically expected not to. The default search space is primarily usedwhen the BS has limited or no knowledge of the channel conditions and/orfor common messages. For this reason, the default search spacecandidates typically carry small payloads at high aggregation levels.

UE-specific search spaces can be used when the channel conditions areknown. In the case of mixed numerologies, the PDCCH numerology would bepart of the search space definition. A considerable amount offlexibility may be desirable, to support the various use cases.Configurability includes, but is not limited to, modulation order, CRCsize, numerology, DRX configuration, message sizes, etc. Aggregationlevels of UE-specific candidates are configurable according to thechannel conditions. For latency critical applications, a terminal can beconfigured with PDCCH resources every subframe while terminals operatingless latency critical applications do not have PDCCH resourcesconfigured every subframe.

2.3.4 Physical Channels, Uplink

Section summary: Physical uplink control channel (PUCCH) is used fortransmission of Fast ACK/NACK information and is transmitted in the lastOFDM symbol(s) of a UL subframe.

TABLE 5 Physical channels in NX Channel Purpose Physical uplink controlUsed for Fast ACK/NACK feedback and channel (PUCCH) potentially other ULcontrol information.

2.3.4.1 Physical Uplink Control Channel (PUCCH)

This channel contains Fast ACK/NACK feedback and potentially other ULcontrol information. Note that it may be possible to eliminate the needfor this physical channel, by instead conveying its payload using dPDCH.The main purpose of dPDCH is to convey scheduling information and CQIfeedback and its payload is modeled as transport blocks. dPDCH includesCRC protection to enable error detection. This format may be suitablefor Fast ACK/NACK feedback (typically consisting only of few bits), suchthat a generalization of dPDCH is sufficient, rather than using a newphysical channel, PUCCH.

PUCCH Design

Regarding the PUCCH payload, up to around 10 bits are assumed. Thispayload size is derived from HARQ ACK/NACK. It is assumed that a singleor a few bits (soft values) are used to provide HARQ ACK/NACK for asingle transport block. Assuming one PUCCH can be used for a fewtransport blocks leads to the assumption of around 10 ACK/NACK bits.

Moreover, transmit diversity of order two is assumed for PUCCH both forMBB and C-MTC UEs. If a UE has more than two transmit antennas, they maybe used for extended transmit diversity and/or beamforming (desirable atleast at higher frequencies). However, some M-MTC UEs can only supportone transmit antenna. Therefore, even 1-antenna PUCCH formats should besupported.

Fast ACK/NACK procedure is beneficial for high data rates, since itenables fast link adaptation and short round trip times. To enable FastACK/NACK feedback in the same subframe, PUCCH is placed at the end ofthe subframe; see Section 2.3.2.1. At minimum, the PUCCH control regionconsists of 1 OFDM symbol, however a few OFDM symbols can be allocatedto PUCCH for extended coverage. Hence, considering the frame structureof NX, 1 to 3 or even 4 OFDM symbols are allocated for PUCCH (due totiming advance, the first symbol in an UL subframe overlaps with lastsymbol of a DL subframe and should be empty, at least if PUCCH is sentimmediately after DL data). Multi-subframe PUCCH can also be considered.

The frequency position of PUCCH could implicitly be given by the DLassignment and potential other information available to the UE;additional signaling could be minimized by that. Candidates to derivethe PUCCH frequency domain location are, e.g., how the scheduling PDCCHis transmitted, frequency location of PDCH, or UE identity. On the otherhand, this introduces coupling between DL and UL which might beundesirable with respect to future-proofness.

Multi-symbol PUCCH for improved coverage can be based on block-spreadingthe one-symbol PUCCH over multiple symbols. To improve capacity,multiple UEs with the same PUCCH duration can share the same frequencyresources by using different block-spreading codes (orthogonal covercodes). This implies that UEs using PUCCH with equal length should begrouped together.

PUCCH is transmitted with the same numerology as UL PDCH.

TDD Specifics

As shown in FIG. 49a , Fast ACK/NAK requires aligned PUCCH transmissionat the end of an UL subframe, leading to DL capacity loss in case ofTDD. Guard periods before and after the UL transmissions are alsorequired to accommodate the switching times, at least one OFDM symbolduration is split as guard time before and after the UL transmission.The UE needs a minimum time to decode the data and prepare a FastACK/NACK; if the processing time given by the guard time is too shortfor providing Fast ACK/NACK at the end of the current subframe, feedbackcan be transmitted at the end of a later subframe.

2.3.5 Physical Channels, Common

Section summary: Physical data channel (PDCH) exists in both UL and DL.It can be configured differently to support various payload types andtransmission modes. Channel coding for MBB may be based on polar codes;however, spatially coupled LDPC codes may also be used, and show similarperformance. For C-MTC, tail-biting convolutional codes are preferreddue their simple decoding and good performance for small block length.

TABLE 6 Physical channels in NX Channel Purpose Physical data A UE canbe configured with multiple PDCH. channel PDCH can be configureddifferently to (PDCH) support transmission of data and controlinformation.

2.3.5.1 Physical Data Channel (PDCH)

PDCH is scheduled via DCI contained in a PDCCH, PDCH, or via asemi-persistent grant and exists on DL, UL, and sidelink (link betweendevices or between eNBs). PDCH can contain user data, DCI, CSI,hybrid-ARQ feedback, and higher-layer control messages. Differentchannel coding schemes exist for PDCH. For example, convolutional codesare used for small payloads with high reliability requirements (e.g.,critical MTC) while higher-performing channel codes are used forcode-words with typical larger payload sizes and lower reliabilityrequirements (e.g., MBB). For more details, see Section 2.3.5.

Data on PDCH can be protected by a retransmission scheme, which can bedisabled for certain PDCH configuration. PDCH with retransmission option(it still can be disabled) is the (retransmitable) rPDCH, while PDCHwithout retransmission option is the (direct) dPDCH. See Section 2.2.2.1for more details on dPDCH and rPDCH. A PDCH can contain zero or onedPDCH and zero or one rPDCH.

PDCH time-frequency resources and transmission format are specified inthe scheduling information. PDCH spans one or multiple subframes and itsfrequency location and bandwidth are variable (as specified in thescheduling information). In the uplink, in a PDCH containing both adPDCH and an rPDCH, dPDCH is mapped to the last OFDM symbol(s) of an ULsubframe since UL control information is transmitted at the end of an ULsubframe. In the downlink, in a PDCH containing both a dPDCH and anrPDCH, dPDCH is mapped to the first OFDM symbol(s) of a DL subframesince DL control information is transmitted at the beginning of a DLsubframe. In general, modulation symbols are mapped frequency firstwithin the scheduled time-frequency resources to resource elements notused for any other purpose. Interleaving in time is not supported sincethis prevents early start of decoding.

PDCH uses the same numerology as used by the scheduling grant.

TABLE 7 Configurations of PDCH Type Comment L1/L2 control Mapped ondPDCH. Configured with information and CSI channel coding for smallpayloads, no hybrid-ARQ Paging and random Mapped on dPDCH. Nohybrid-ARQ, access response self-contained sync signal MBB Mapped onrPDCH. Configured with high performing channel codes and hybrid-ARQC-MTC Mapped on dPDCH or rPDCH. Configured with convolutional codes andoften without hybrid-ARQ Contention-based Configured to enablecontention-based access

Paging and Random Access Response

In this configuration, fine-synchronization cannot rely on the SignatureSequence (SS) signal but requires a self-contained sync and referencesignal (to support non-co-located transmission points of SS and randomaccess response or paging and/or different antenna weights). Paging andrandom access response may use the same PDCH configuration. Paging andrandom access response are transmitted on dPDCH.

MBB

Different configurations for different MIMO modes, e.g.,reciprocity-based MIMO vs. feedback-based MIMO exist. Channel coding canbe based on polar codes or spatially-coupled LDPC codes. MBB data aremapped to rPDCH.

C-MTC

Channel coding in this configuration is convolutional coding. Due tostrict latency requirements, hybrid-ARQ can be disabled. C-MTC data aremapped to rPDCH or dPDCH. For achieving low block error rate withoutexhausting the available link budget, diversity over fading isimportant. Diversity may be achieved via spatial diversity, usingmultiple transmit and receive antennas, or frequency diversity usingmultiple resource blocks of independent fading coefficients. Due to lowlatency requirement, it is however, impossible to exploit timediversity. Furthermore, for the case of transmit and frequencydiversity, channel codes need to have sufficient minimum Hamming or freedistance to take full advantage of the diversity.

2.3.5.2 Channel Coding for PDCH

Section summary: For MBB Spatially-coupled (SC) LDPC codes and polarcodes are attractive candidates. Both provide higher throughput formoderate-to-large block lengths, have lower complexity per transmittedinformation bit, and provide substantially higher decoding throughputthan Turbo codes.

For C-MTC short—and thus low complexity—decoding is important. LTEconvolutional codes fulfill the C-MTC requirements w.r.t. reliabilityand latency.

MBB

The LTE standard deploys Turbo codes due to their remarkableperformance—they approach capacity within 1 dB gap over generalchannels. However, recent advances in channel coding theory have broughttwo classes of channel codes that—unlike Turbo codes—provably achievethe capacity for very large block lengths: 1) Spatially-coupled (SC)LDPC codes and 2) polar codes. These two classes of codes outperformTurbo codes from several aspects, and are thus the two most attractivecandidates for 5G MBB systems.

Listed below are some advantages of polar codes and SC-LDPC codes overTurbo codes:

-   -   1. Both polar and SC-LDPC codes have higher throughput for        moderate-to-large block lengths n (n>˜2000 for polar codes).        Performance gap compared to Turbo codes increases as n gets        larger.    -   2. For short block lengths (n˜256), polar codes outperform all        other known classes of codes including Turbo codes and SC-LDPC        codes.    -   3. Polar codes have lower encoding and decoding complexity per        transmitted information bit (and consequently higher energy        efficiency) compared to both LDPC and Turbo codes.    -   4. SC-LDPC codes have low error floor. Polar codes don't have an        error floor.    -   5. Both polar and SC-LDPC codes have substantially higher        decoding throughput in bits/s obtained at the decoder output        [Hon15b].        A brief overview of these two classes of codes is provided        below.

2.3.5.2.1 LDPC and Spatial-Coupled (SC) LDPC Codes

Regular LDPC codes with constant variable node degree and check nodedegree were first proposed by Gallager in 1962. They are asymptoticallygood in the sense that their minimum distance grows linearly with blocklength when the variable node degree is chosen to be larger than 2. Forinstance, FIG. 58a shows a graphical representation of the parity checkmatrix of a (3,6)-regular LDPC code of block length 6 with variable nodedegree of 3 and check node degree 6, where black circles representvariable nodes and white circles represent check nodes. Due to the useof suboptimal iterative decoding, however, their performances are worsethan Turbo codes in the so-called waterfall region, making themunsuitable for power-constrained applications as typically encounteredin cellular networks.

There are two design improvements that enable LDPC codes to be adoptedin several communication standards. First, optimized irregular LDPCcodes, with a variety of different node degrees, showcapacity-approaching performance in the waterfall region and can achievebetter performance than Turbo codes in this region. The second isprotograph-based construction of irregular LDPC codes. It has beenobserved that protograph-based irregular LDPC codes often have betterperformances than unstructured irregular ones with the same degreedistributions. In spite of their success, irregular LDPC codes, unlikeregular LDPC codes, are normally subject to an error floor, i.e., aflattening of the bit error rate (BER) curve that yields poorperformance at high SNRs, making them undesirable in applications asdata storage, critical MTC, and so on.

Spatially-coupled LDPC (SC-LDPC) codes, proposed by Felstrom andZigangirov, are the first class of codes that achieve the capacityuniversally for a large class of channels with low-complexity encodingand decoding. They are simply constructed by starting from a sequence ofL independent (regular) LDPC codes, which are then interconnected byspreading the edges over blocks of different time instants (see FIG. 58c). SC-LDPC codes combine the best features of well-optimized irregularand regular LDPC codes in a single design: capacity achieving and linearminimum distance growth. Further, these codes are very suitable tosliding-window decoding, thereby improving the decoding latency.However, their performances are worse than the well-optimized irregularLDPC codes at short and intermediate block lengths (n<1000) and attarget block error rate 0.01 or less, where error floor can become asignificant problem.

2.3.5.2.2 Polar Codes

Polar Codes, proposed by Arikan, are the first class of constructivecodes that achieve symmetric (Shannon) capacity (capacity for binaryinput symbols with symmetric distribution) of binary-input discretememoryless channel using a low-complexity encoder and low-complexitysuccessive cancellation decoder. At the heart of polar codes is thephenomenon of channel polarization, whereby n identical and independentinstances of a given channel are transformed into another set ofchannels that are either noiseless channels (with capacity close to 1)or pure-noise channels (with capacity close to 0) for asymptoticallylarge block lengths. Furthermore, the fraction of “good” channelsapproaches the symmetric capacity of the original channel. A polar codethen comprises sending information bits over the good channels, whilefreezing the input to the bad channels with fixed values (typicallyzeros) known to the receiver. The transformation on a block of n channelinstances is obtained by recursively coupling two blocks of transformedchannels of size n/2. This is illustrated in FIG. 59, which shows therecursive encoding structure of polar codes. (The tilted dash lines areshown only for illustration of underlying butterfly operations). As aresult, the encoding process of polar codes comprises recursiveapplications of a simple butterfly operation commonly used in FFT andthus can be implemented efficiently with computational complexitygrowing only in the order of n log n.

In theory, polar codes can achieve the best possible performance(Shannon capacity) with just a simple successive cancellation decoder.However, in practice, polar codes require a modified successive decoder(list decoder) to achieve performance comparable or even better thanstate-of-the-art LDPC codes. In a list decoder, memory requirementsscale linearly with both the list size L (typically in the order of 30)and the block size n (as for SC-LDPC and Turbo), while computationalrequirements grow as Ln log n.

2.3.5.2.3 Comparison of Channel Codes

Table 8 shows a brief comparison of Turbo codes, SC-LDPC codes, andpolar codes in terms of complexity and decoding throughput. The firstrow specifies the relationship between the number of requiredencoding/decoding operations where δ represents the difference betweenthe channel capacity and the code rate. Polar codes have the lowestcomplexity that increases logarithmically with 1/δ, whereas for bothSC-LDPC codes and Turbo codes this dependence is of the linear order. Interms of the decoding throughput, the hardware implementation of SC-LDPCcodes achieves significantly higher decoding throughput compared toTurbo codes. Note that while decoding throughput of polar codes appearsto be the highest, the results shown in Table 8 are obtained with a FPGAimplementation. The decoding throughput of polar codes with a hardwareimplementation remains to be evaluated.

TABLE 8 Comparison of complexity and decoding throughput for differentcodes SC-LDPC Polar Turbo Complexity Θ(1/δ) Θ(log (1/δ)) Θ(1/δ) (cannot(# operations achieve to be at δ-gap capacity) to the capacity) Decoding130.6 Gbps, 254.1 Gbps 2.3 Gbps, throughput 11ad LDPC (FPGA) 3GPP TC(1024, 512) code

Beyond performance and complexity, other important requirements on goodcodes are their rate-compatibility and ability to be used for hybridautomatic repeat request with incremental redundancy (HARQ-IR).Communication systems that operate over wireless channels with varyingquality require channel codes with different rates, in order to adapt tochannel variations. To reduce the storage requirement for a potentiallylarge set of codes, these codes should be derived from a single parentcode of a fixed rate, also known as rate-compatible codes. Modernwireless communication systems often use a HARQ-IR protocol. Incrementalredundancy systems require the use of rate-compatible codes where theset of parity bits of a higher rate code is a subset of the set ofparity bits of a lower rate code. This allows the receiver that fails todecode at a rate chosen at the transmitter, to request only additionalparity bits from the transmitter, greatly reducing the encoder/decodercomplexity. One possible approach to rate-compatibility is puncturing,whereby some of the bits in the code of the lowest rate (parent code)are punctured in order to obtain higher rate codes. However, puncturingof polar codes incurs a performance loss.

The method described herein uses parallel-concatenated polar codeswhere, in order to sequentially transmit at rates R₁>R₂> . . . >R_(K),in each transmission block i, a new polar encoder of rate R_(i) andblock length n_(i) is used. The concatenated polar code is decoded by asequence of K polar decoders. The parallel-concatenated encoder anddecoder structures are shown respectively in FIG. 60 and FIG. 61, forK=2 transmissions. Note that the polar decoder rate is used first todecode the information bits in the two boxes at the right of each set ofillustrated bits. These bits are then used in the polar decoder of rateR₁ to turn it into a polar decoder of rate R₂ that is supported by thechannel, thereby enabling the decoding of the rest of the informationbits.

Having K transmissions implies that the channel can only support rateR_(K), and that rates R₁, R₂, . . . , R_(K−1) are not supported by thechannel. Therefore, the difficulty lies in decoding the polar codes sentin first K−1 transmissions at rates R₁, R₂, . . . , R_(K−1). To maketheir decoding possible, the nested property of polar codes isexploited.

This approach achieves the capacity as the block length grows large, forany number of retransmissions K.

Critical-MTC

LTE tail-biting convolutional codes—even if used together with a decoderthat is optimized for decoding speed rather than performance—achievevery low block error rates, making them an attractive choice for C-MTC.Furthermore, convolutional codes don't have an error floor, an importantcharacteristic for very low target error rates.

Lately it has also been observed that polar codes perform very well evenfor short code blocks. Accordingly, polar codes are another choice thatcan be applied to C-MTC.

Diversity is important to achieve high reliability at reasonable SNRlevels. The channel code should provide sufficient free distance orminimum Hamming distance to ensure that full diversity can be harvested.

2.3.6 Reference and Synchronization Signals, Downlink

Section summary: Signature sequences (SS) are used to indicate an entryin AIT and to establish some level of subframe synchronization for atleast random access preamble transmission. SS are constructed in asimilar way as the synchronization signal in LTE by concatenation of aprimary signature sequence and a secondary signature sequence.

The combination of time and frequency synchronization signal (TSS) andbeam reference signal (BRS) is used to obtain time/frequency/beamsynchronization after initial synchronization and access by SS andPRACH. This combined signal is also referred to as MRS (mobilityreference signal) and is used for handover (between nodes and beams),transitions from dormant to active states, mobility, beam tracking andrefinement, etc. The MRS is constructed by concatenating TSS and BRSsuch that MRS is transmitted within a single DFT-precoded OFDM symbol.

Channel state information reference signals (CSI-RS) are transmitted inDL and are primarily intended to be used by UEs to acquire CSI. CSI-RSare grouped into sub-groups according to the possible reporting rank ofthe UE measurement. Each sub-group of CSI-RS represents a set oforthogonal reference signals.

Positioning reference signals (PRS) aid positioning. Already existingreference signals should be reused for PRS purposes. On top of that—ifrequired—modifications and additions can be done to improve positioningperformance.

TABLE 9 DL reference and synchronization signals in NX Signal PurposeSignature sequence (SS) Used to synchronize time and frequency forrandom access. Provides index to AIT table. Mobility and accessConcatenation of one TSS and one BRS reference Signal (MRS) Time andfrequency Used to synchronize time (OFDM symbol synchronization signaltiming) and coarse frequency offset (TSS) estimation in a beam. Beamreference Used for measurements on beam signal (BRS) candidates toenable active mode mobility. Also used for frame and subframe timing.Demodulation reference Demodulation reference signals for signal (DMRS)for PDCCH PDCCH Channel state information Used for channel statemeasurements to reference signal (CSI-RS) aid rank and MCS selection.Positioning reference signal To aid positioning. (PRS)

2.3.6.1 Signature Sequence (SS)

Basic functions of SS are one or more of:

-   -   to obtain the SSI, which is used to identify the relevant entry        in AIT;    -   to provide coarse frequency and time synchronizations for the        following initial random access and relative AIT allocation;    -   to provide a reference signal for initial layer selection (to        select which SS transmission point for a UE to connect, based on        the path-loss experienced by SS's);    -   to provide a reference signal for open-loop power control of the        initial PRACH transmission; and    -   to provide a coarse timing reference used for assisting the UE        in inter-frequency measurements and also possible beam finding        procedure. The current assumption is that SS transmissions are        synchronized within a ±5 ms uncertainty window unless explicitly        indicated otherwise. The period of SS is supposed to be in the        order of 100 ms, which however may be varied, depending on the        scenarios.

It is noted that the number of the candidate sequences needs to be largeenough to indicate any entry in AIT. Taking the terminal detectioncomplexity into account, the number of SS sequences is 2¹²,corresponding to 12 bits for reuse 1 of the sequences, or less if lessaggressive sequence reuse is required. Note that the number of bits tobe carried depends on requirements. If the number of bits increasesbeyond what can be carried by sequence modulation, a variation of the SSformat is desirable. In this case, one code-word containing the extrabits beyond what the sequences can carry can be appended. This block,following an SS transmission, is named SS block (SSB). The content inthis block is flexible and contains the other relevant information bits,which need a periodicity in the order of 100 ms. For example, they canbe the “AIT pointer”, which indicates the time and band where theterminals can find the AIT and even the transmission format of AIT toavoid full blind detection.

The sequence design for SS can follow the TSS/BRS sequence design,described in Section 2.3.6.3 and Section 2.3.6.4, since they wouldprovide the coarse synchronization function before the initial randomaccess, as introduced in Section 3.2.5.2.

To support the massive analog beamforming, a fixed absolute timeduration, e.g., 1 ms, is reserved to sweep multiple analog beams.

For SS numerology the same discussion as in Section 2.3.3.1 for PACHapplies. However, the current design does not enable CP lengthdetection.

2.3.6.2 Mobility and Access Reference Signal (MRS)

In the process of acquiring system access information (acquiring systeminformation and detecting a suitable SSI), the UE gets time andfrequency synchronized towards one or several nodes by using SS. Thelatter is achieved in the case of system access information transmittedsimultaneously from several nodes in an SFN (single frequency network)manner.

When the UE enters active mode, it targets to receive or transmit with ahigh data rate connection, in which it might need more accuratesynchronization and perhaps beamforming. Here, the mobility and accessreference signal (MRS) is used. A UE might also need to change whichnode it is connected to e.g., from a node used to transmit system accessinformation to another node capable of beamforming. Furthermore, the UEmight also change carrier frequency or numerology to higher sub-carrierspacing and shorter cyclic prefix when moving to certain operationalmodes in active mode.

The MRS is constructed in order to do time and frequency offsetestimations as well as estimation of best downlink transmitter andreceiver beams towards an “active mode access point”. Frequency accuracyand timing provided by MRS is probably not sufficient for high-ordermodulation reception and finer estimation may be based on DMRS embeddedin PDCH and/or CSI-RS.

The MRS is constructed by concatenating a time and frequencysynchronization signal (TSS) and a beam reference signal (BRS) in timeinto one OFDM symbol, as illustrated in FIG. 62. This construction canbe done as a DFT-precoded OFDM symbol with cyclic prefix. With both TSSand BRS in the same OFDM symbol, the transmitter can change itsbeamforming between each OFDM symbol. Compared to having separate OFDMsymbols for TSS and BRS, the time required for scanning a set of beamdirections is now halved. Both TSS and BRS thus have shorter timedurations as compared to separate OFDM symbols for each of them. Thecost for these shorter TSS and BRS is reduced energy per signal and thusreduced coverage, which can be compensated by increasing the bandwidthallocation, repeating the signal, or increasing the beamforming gain bymore narrow beams. Where mixed numerology is supported, the numerologyused for MRS is the same as that one used by the UE for which MRS arescheduled. In the event that multiple UEs within the same beam usedifferent numerologies, MRS cannot be shared and MRS should betransmitted separately for each numerology.

Different beamforming configurations can be used to transmit the MRS indifferent OFDM symbol, e.g., in each of the three symbols shown in FIG.62. The same MRS might also be repeated several times in the same beamin order to support analog receiver beamforming. There are only one orfew TSS sequences, similar to PSS in LTE. The UE performs matchedfiltering with the TSS sequence to obtain OFDM symbol timing estimation;TSS should therefore possess good a-periodic auto-correlationproperties. This sequence might be signaled by system information suchthat different AP (Access Points) can use different TSS sequences.

The MRS (as constructed by TSS+BRS) signal package is usable for allactive mode mobility-related operations: first-time beam finding,triggered beam mobility update in data transmission and monitoringmodes, and continuous mobility beam tracking. It may also be used forthe SS design, see section 2.3.6.1.

2.3.6.3 Time and Frequency Synchronization Signal (TSS)

The TSS sequence is identical in all OFDM symbols and beam directionstransmitted from a base station, while BRS uses different sequences indifferent OFDM symbols and beam directions. The reason for havingidentical TSS in all symbols is to reduce the number of TSS which a UEmust search in the quite computational complex OFDM symbolsynchronization. When the timing is found from TSS, the UE can continueto search within a set of BRS candidates in order to identify the OFDMsymbol within a subframe as well as best downlink beam. Best downlinkbeam can then be reported by USS as described in section 2.3.7.2.

One choice for such sequences is the Zadoff-Chu sequences as used forPSS in LTE release 8. However, these sequences are known to have largefalse correlation peaks for combined timing and frequency offsets.Another choice is differential coded Golay sequences, which are veryrobust against frequency errors and have small false correlation peaks.

2.3.6.4 Beam Reference Signal (BRS)

The BRS is characterized by different sequences transmitted in differenttransmitted beams and OFDM symbols. In this way, a beam identity can beestimated in the UE for reporting to the access node.

An identification of OFDM symbol within the subframe is desirable if thetiming difference between SS and active mode transmissions is large.This might occur for numerologies with short OFDM symbols, largedistance between the node transmitting system access information and thenode in which the UE is supposed to transmit user data (in case thesenodes are different), or for unsynchronized networks. Thisidentification can be done if different BRS sequences are used fordifferent OFDM symbols. However, in order to reduce computationalcomplexity, the number of BRS sequences to search for should be low.Depending on the OFDM symbol index uncertainty, a different number ofBRS sequences may be considered in the blind detection of the UE.

The BRS can be a dedicated transmission to one UE or the same BRS mightbe configured for a group of UEs. A channel estimate from TSS can beused in a coherent detection of BRS.

2.3.6.5 Channel State Information RS (CSI-RS)

CSI-RS are transmitted in DL and are primarily intended to be used byUEs to acquire channel state information (CSI) but can also serve otherpurposes. The CSI-RS may be used for one or more of (at least) thefollowing purposes:

-   -   1. Effective channel estimation at the UE: Frequency selective        CSI acquisition at the UE within a DL beam, e.g., used for PMI        and rank reporting.    -   2. Discovery signal: RSRP type measurement on a set of CSI-RS        reference signals. Transmitted with a time density according to        large scale coherence time of the relevant (DL) channels.    -   3. Beam refinement and tracking: Get statistics about the DL        channel and PMI reporting to support beam refinement and        tracking. PMI does not need to be frequency selective.        Transmitted with a time density according to large scale        coherence time of the relevant (DL) channels.    -   4. For UE transmit beam-forming in UL assuming reciprocity.    -   5. UE beam-scanning for analog receive beam-forming in DL        (similar requirements to 1) or 3) depending on use-case).    -   6. To assist fine frequency/time-synchronization for        demodulation.

In some cases, not all of the above estimation purposes needs to behandled by CSI-RS. For example, frequency offset estimation cansometimes be handled by DL-DMRS, beam-discovery is sometimes handled byBRS. Each CSI-RS transmission is scheduled and can be in the samefrequency resources as a PDCH DL-transmission or in frequency resourcesunrelated to the PDCH DL-data transmissions. In general, nointerdependence between CSI-RS in different transmissions can beassumed, and hence the UE should not do filtering in time. However, a UEcan be explicitly or implicitly configured to assume interdependencebetween CSI-RS, for example, to support time-filtering of CSI-RSmeasurements (e.g., in 2 above) and also interdependence to othertransmissions including PDCCH and PDCH. In general, all UE filteringshall be controlled by the network, including filtering of CSI in time,frequency and over diversity branches. In some transmission formats,CSI-RS is situated in a separate OFDM symbol to better support analogbeam-forming both for base station TX and UE RX. For example, to supportUE analog beam-scanning (item 5 above) the UE needs multiple CSI-RStransmissions to measure on in order to scan multiple analog-beamcandidates (4 in Example 2 in FIGS. 63A and 63B).

CSI-RS are grouped into sub-groups related to the possible reportingrank of the UE measurement. Each sub-group of CSI-RS represents a set oforthogonal reference signals that can use code multiplexing; only alimited set of highest ranks is supported in this fashion e.g., 2, 4 and8. Multiple sub-groups within a group are created by assigningorthogonal sets of resource elements to the sub-groups. Measurementswithin a sub-group is for good correspondence with D-DMRS and separateresource elements is used to better support measurements on non-servingbeams. The main enabler for allowing CSI-RS to fulfill requirements 1 to6 above is to support flexible configuration of CSI-RS. For example,frequency offset estimation is enabled by configuring time repetition.The usage of CSI-RS or DMRS for frequency offset estimation is alsopossible. The CSI-RS groups and sub-groups design should allow efficientmultiplexing of UEs with different configurations. Consider in FIG. 63Bthe three examples:

-   -   In Example 1, the UE is measuring on 3 CSI-RS sub-groups; 1 of        rank 4; and 2 of ran k2;    -   In Example 2, the UE is configured with 4 consecutive identical        resources, e.g., to support requirement 5 but sub-sampled in        frequency domain;    -   In Example 3, the UE is rate matching around the CSI-RS        sub-group on the first OFDM symbol containing CSI-RS but not        around the 2 sub-groups on the second OFDM symbol containing        CSI-RS.

2.3.6.6 Positioning Reference Signal (PRS)

In order to support a flexible framework for positioning, the PRS can beseen as a potentially UE specific configuration of a reference signal.The PRS convey an identifier associated to a node or a set of nodes, ora beam, while also enabling time of arrival estimation. This means thatother signals, such as SS, TSS, BRS, etc., can fulfil some requirementsof the PRS. Furthermore, the PRS can also be seen as extensions of suchsignals.

For example, based on FIG. 62, a PRS can be configured as the TSS/BRS ofsymbol 0 for one UE, while another PRS can be configured as TSS/BRS ofsymbols 0,1,2 (same BRS in all three symbols in time) for another UE. Atthe same time, the TSS/BRS of symbol 0 is used for time synchronizationand beam finding by other UEs.

2.3.7 Reference and Synchronization Signals, Uplink

Section summary: Physical random access channel (PRACH) preamble isconstructed by concatenating several short sequences, each sequencebeing of the same length as an OFDM symbol for other NX UL signals.These short sequences can be processed using the same FFT sizes as otherUL signals thus avoiding the need for dedicated PRACH hardware. Thisformat also enables handling of large frequency offsets, phase noise,fast time varying channels, and several receiver analog beamformingcandidates within one PRACH preamble reception.

Uplink synchronization signal (USS) is used to obtain ULsynchronization. The design is similar to PRACH but it is notcontention-based, and is used for timing estimation and beam reportingin uplink after initial access by SS and PRACH, e.g., at handoverbetween nodes and carriers. This timing estimation is desireable due toUE specific round trip time depending on distance between UE and basestation, such that a timing advance command can be sent to the UE.

Reciprocity reference signals (RRS) are uplink reference signals andused to obtain CSI-R (receiver-side CSI) and CSI-T (reciprocity basedtransmitter-side CSI) at the base station but also for UL demodulation;thus, they can be viewed as a combination of SRS and DMRS. To avoidpilot contamination, a large number of orthogonal reference signals arerequired. If RRS are also used for UL channel estimation innon-reciprocal setups a renaming of RRS is likely.

TABLE 10 UL reference and synchronization signals in NX Signal PurposePRACH preamble Initial transmission of UE. Contention-based such thatthe PRACH preamble should be detected with high reliability. Timing andreceiver beam estimation. Uplink synchronization Used for uplink timeand frequency synchron- signal (USS) ization and indicating of bestdownlink beam. Reciprocity reference Used to estimate the UL channel andto set the signal (RRS) DL pre-coding in the transmitter in reciprocity-based MIMO. Demodulation reference Demodulation reference signals forPUCCH signal (DMRS) for PUCCH

2.3.7.1 Physical Random Access Channel (PRACH) Preamble

Random access is used for initial access for a UE includingtiming-offset estimation at the base station. The random-access preambleshould thus be detected with high probability and low false-alarm rateby the base station while at the same time providing accurate timingestimates.

The numerology used for the PRACH preamble is specified in AIT.

The computational complexity of FFT (Fast Fourier Transform) processingin an OFDM based receiver is large with a large amount of receiverantennas. In LTE release 8, FFTs of different sizes are used for userdata and random-access preambles, requiring dedicated FFTs to beimplemented for random-access reception. (Even LTE PRACH preamble whichis defined with a dedicated (very large) IFFT can be received at thebase station with signal processing procedures only requiring standardphysical channel FFTs, at the cost of a small performance penalty.)

Within NX, a 5G random-access preamble format is used, based on a shortsequence of the same length as the length of the OFDM symbols that areused for other uplink physical channels, such as user data, controlsignaling, and reference signals. The preamble sequence is constructedby repeating this short sequence multiple times. FIG. 64 illustrates thepreamble format and a detector with long coherent accumulation.

A preamble detector with FFTs of the same size as for other uplinkchannels and signals can be used. In this way, the amount of specialrandom-access related processing and hardware support is significantlyreduced.

As example, twelve repetitions of the short sequence are coherentlyadded within the receiver structure of FIG. 64. However, a receiver canalso be designed in which only a few repetions are coherently addedbefore the absolute square operation followed by a non-coherentaccumulation. In this way a receiver can be constructed which is robustagainst phase noise and time varying channels.

For analog beamforming, the beamforming weights can be changed duringpreamble reception such that the number of spatial directions isincreased for which preamble detection is done. This is done by analogbeamforming before FFT, and only including those FFTs in the coherentaccumulation for which the same beamforming is used. Here, the coherentaccumulation is traded against beamforming gain. Also, with shortercoherence accumulation, the detection is more robust against frequencyerrors and time varying channels. The number of available preamblesequences is reduced when reducing the length of the sequence, ascompared to the very long sequence used for PRACH preambles in LTErelease 8. On the other hand, the use of narrow beamforming in a 5Gsystem reduces the impact of interference from other UEs. Otherpossibilities for avoiding congestions on the PRACH preambles includeuse of frequency shifted PRACH preambles, and the use of several PRACHfrequency bands and several PRACH time intervals.

The receiver structure illustrated in FIG. 64 can be used for detectionof delays up to the length of one short sequence. A somewhat modifiedreceiver structure is desirable where some additional processing isadded for detections of large delays due to large distances between UEand base station. Typically, more FFT windows are used after and beforethose illustrated in FIG. 64, with simple detectors of the presence ofshort sequences in those additional FFT windows.

2.3.7.2 Uplink Synchronization Signal (USS)

The UE needs uplink time synchronization when changing access node orcarrier frequency resulting in changed numerology. Assuming that the UEis already time synchronized in downlink (by MRS), the timing error inuplink is mainly due to propagation delay between the access point andthe UE. Here, a USS (uplink synchronization signal) is proposed with asimilar design as PRACH preamble, see section 2.3.7.1. However, USS isnot contention-based as in contrast to the PRACH preamble. Thetransmission of USS is thus only done after a configuration from thebase station that the UE should search for MRS and respond with USS.

FIG. 65 illustrates USS in relation to MRS and uplink grant includingtiming advance USS is intended for uplink timing advance calculation,uplink frequency offset estimation, and UL beam identification. The UEmight also select USS sequence depending on OFDM symbol for best MRS. Inthis way the access point gets information of best downlink beam.

The time and frequency allocation of USS can be done by higher layersignaling from the node transmitting system access information.Alternatively, a mapping is defined between BRS sequences to a“count-down” number until USS resource. In this case, different BRSsequences are used in different OFDM symbols. The UE then gets theposition of the USS windows by detecting BRS sequence. If mixing ofnumerologies is supported the numerology used for USS is specified inthe configuration/grant of USS.

2.3.7.3 Reciprocity Reference Signal (RRS)

Reciprocity reference signals are transmitted in uplink and areprimarily targeting massive-MIMO deployments that can benefit from radiochannel reciprocity; see Section 3.4.3.3. The most common use case isTDD operation, but for extensive MU-MIMO in UL, RRS is useful even iffull reciprocity cannot be assumed. In the uplink, RRS is intended to beused both for coherent demodulation of physical channels and for channelsounding as part of CSI-R acquisition at the base station. It can benoticed that CSI-R acquisition does not rely on reciprocity and is thusrepresentative for both TDD and FDD. In the downlink, CSI-T is extractedfrom coherent (uplink) RRS, thereby mitigating the need for explicit CSIfeedback based on downlink reference signals when channel reciprocitycan be assumed. The RRS used for coherent demodulation is precoded inthe same way as data/control. RRS used for sounding can be transmittedin subframes carrying uplink physical channels (as in LTE) as well as insubframes specifically designed for sounding only.

Pilot contamination is seen as a major performance degradation source inmassive-MIMO and occurs when a large number of overlaid receivedreference signals are non-orthogonal. Non-orthogonality in uplink canstem from reuse of reference signal sequences among UEs or receivedreference signals arrive outside the cyclic prefix due to uplinktransmissions synchronized to other base stations. The RRS designprovides a large number of orthogonal sequences or at least with verylow mutual cross-correlation. It might be beneficial to use cyclicprefix that also accounts for pilot transmissions originating fromneighbor cells (trade-off between additional cyclic prefix overhead vs.pilot contamination). Orthogonality between RRS sequences is obtainedvia: (i) equally spaced cyclic time shifts, (ii) use of orthogonal covercodes (OCC), and (iii) of “transmissions comb” (a.k.a. interleavedFDMA).

The transmission bandwidths of RRSs in the system vary with UL/DLscheduling demands among users as well as being dependent on uplinktransmit power limitations. Hence, the RRS design needs to handle a vastnumber of RRS multiplexing scenarios in which orthogonality should bepreserved among users/layers to avoid pilot contamination. In LTE, thesequence length of e.g., an UL DMRS directly relates to the uplinkscheduling bandwidth which requires either equally long sequences (andthus equal scheduling bandwidth) or relying on OCC for orthogonalityamong reference signals. Imposing same scheduling bandwidth is thus notattractive, and relying only on OCC is not sufficient for obtaining alarge number of orthogonal reference signals. Instead of letting thebase sequence lengths be associated with the scheduling bandwidth, onecould concatenate narrowband RRS sequences such that the overall RRSbandwidth is a multiple, or a sum, of narrowband RRSs. This impliespiecewise orthogonality over the whole RRS bandwidth. One may inaddition to concatenating narrowband RRSs also use transmission combs asa mechanism to preserve orthogonality when, e.g., RRS sequencesoriginates from base sequences of different lengths.

Note that when the UE has more RX antennas and also is capable ofapplying UL beamforming, RRS beamforming may be applied to boost thereceived energy and help the base station to achieve a better channelestimation. This, on the other hand, would result in that the basestation estimates the “effective” channel including the UE beamforming.

FIG. 66 shows an example of how to implement multiple orthogonal RRSacross different portions of the system bandwidth using a combination ofcyclic shifting, transmission combs, and OCC. FIG. 66a shows differenttransmission combs. The right-hand side of FIG. 66b shows different OCCused in different bandwidth locations; in the upper part an OCC oflength 2 is used, in the second part of length 4, etc.

Numerology of RRS is specified in the configuration/grant of RRS.

2.3.7.4 Demodulation Reference Signals (DMRS) for PUCCH

With the use of an OFDM structure for uplink transmissions, the RS canbe frequency multiplexed with data. To enable early decoding referencesignals should at least be sent in the first OFDM symbol of PUCCH, formulti-symbol PUCCH formats additional reference signals in later symbolsmight be needed as well. Since PUCCH is always transmitted in the lastOFDM symbol(s) of a subframe, PUCCH transmissions from differentterminals interfere if they use the same frequency, e.g., inter-cellinterference or multi-user MIMO interference.

2.3.8 Reference and Synchronization Signals, Common

Section summary: PDCH has its own set of demodulation reference signals(DMRS). Orthogonal DMRS are realized via a combination of orthogonalcover codes (OCC) and mapping DMRS sequences to transmission combs.

TABLE 11 Reference and synchronization signals in NX common for DL andUL Signal Purpose Demodulation reference signal Demodulation referencesignals (DMRS) for PDCH for PDCH DL and UL

2.3.8.1 Demodulation Reference Signal (DMRS) for PDCH

DMRS is transmitted both in DL and UL multiplexed with a physicalchannel and serves the purpose of demodulation of PDCH transmissions. InUL, DMRS is sometimes not needed when RRS is present—e.g., see UL datatransmission in subframe n+7 after purple RRS in subframes n+5 and n+6in FIG. 67—but it is anticipated that for very small messages and inbeam-based transmissions (see Section 3.4.3.2), DMRS is stillpreferable. FIG. 67 shows a schematic view of DMRS on a small scaleperspective with the first 9 subframes for a single UE. FIGS. 68A and68B show a large scale view of the same subframes. In the firstbeam-based period shown in FIGS. 68A and 68B, limited CSI is used toprecode DMRS and data but in the reciprocity-period rich channelknowledge is used for advanced precoding of DMRS and data. Additionaldetails are provided in Section 3.4.3.3. Physical mapping to resourceelements depends on the transmission format.

Any initial subframe PDCH will contain DMRS, but later subframes in asubframe aggregate may not contain DMRS if DMRS based channel estimatesfrom a previous subframe are still valid for demodulation. For example,see subframes n and n+3 in FIG. 67. DMRS are configured UE-specific, buta set of users can share the same configuration to enable e.g.,broadcast. In aggregated subframes the UE may assume that precoding isnot changed and interpolation may be done within a subframe. OrthogonalDMRS are created using orthogonal cover codes in frequency and in somecase cover codes are also used in time. Two examples when time covercodes are desirable is for fine frequency offset estimation and forextended coverage. It is assumed that the cover codes are optimized forthe use-case that a transmission is from a single transmission point.The cover codes can also be mapped to comb-structures, on differentcombs different sets of cover-codes are used with low-cross correlationproperties. Different combs are anticipated when large scale channelproperties can vary (including frequency offset). The availableorthogonal DMRS can be used both for SU-MIMO and MU-MIMO. DMRS indifferent beams are not necessarily orthogonal but rather rely onspatial separation and low cross-correlation properties between the DMRSsequences in different sets of orthogonal DMRS.

If PDCH has multiple transport blocks the DMRS are shared, for example,dPDCH and rPDCH use the same DMRS but are associated with differenttransmission formats, for example, diversity for dPDCH and spatialmultiplexing for rPDCH. For PDCH, the DMRS are transmitted withsufficient density early in a subframe aggregate or in UL early inrelation to a duplex switch (in some cases in a previous transmissionperiod) to support early demodulation and decoding. In time, DMRS aretransmitted in different subframes according to the coherence time,e.g., repeated for longer transmissions and/or high mobility users.Repetition can also be needed to track time/frequency drift in hardware.In frequency, the DMRS are repeated in resource blocks according to theeffective coherence bandwidth and the targeted DMRS energy density.Observe that effective coherence bandwidth increases due to channelhardening when using reciprocity—see last DL transmission in FIGS. 68Aand 68B, as well as the discussion in section 3.4.3.3. In such cases, itis expected that DMRS in DL can be sparser than in cases where RRS arenot present. The repetition is typically explicitly signaled in relationto the number of subframes in the TTI, or in some cases implicitly forshared pre-allocated channels.

3 Technologies and Features

The prime purpose of this section is to describe how to use thefunctions, procedures, channels, and signals described in Section 2 torealize NX features. However, new functions, procedures, channels, andsignals that have not been generally agreed may still be documented inthis section. In some cases, new functions, procedures, channels, andsignals are introduced as new technologies, and solutions are discussedhere. Note that not all of these are necessarily implemented in a NXprotocol stack.

3.1 Low Latency and High Reliability

The purpose of this section is to describe how NX enables use casesrequiring reliable real-time communication, with a special focus onchallenging critical MTC (C-MTC) use cases.

3.1.1 Background and Motivation for Reliable Low Latency

A range of 5G machine-type communication (MTC) use cases, such as smartgrid power distribution automation, industrial manufacturing andcontrol, intelligent transportation systems, remote control of machines,and remote surgery, are characterized by the need for communication withhigh requirements on latency, reliability, and availability. We normallyrefer to such use cases as mission-critical MTC use cases (C-MTC), whichis in line with the vision of the International TelecommunicationsUnion, which refers to C-MTC as “ultra reliable and low latencycommunication.”

Low latency is also desirable to support high end user throughput forTCP based applications which has, e.g., been the main argument forlatency reduction in LTE. This is, however, expected to be handled wellwith the baseline NX design as described in Chapter 2, and is notdiscussed further in this section.

3.1.2 Requirements and KPIs Latency

For the latency discussion over the NX radio interface, this sectionrefers to the RAN User plane latency (or short RAN latency), as definedin section 4.2, unless otherwise mentioned. The RAN latency is theone-way transit time between an SDU packet being available at the IPlayer in the user terminal/base station and the availability of thispacket (protocol data unit, PDU) at IP layer in the base station userterminal. User plane packet delay includes delay introduced byassociated protocols and control signaling assuming the user terminal isin the active state.

Most delay sensitive use-cases can be supported with a RAN latency of 1ms, but there are a few examples of one-way latency requirements of 100μs, e.g., in factory automation. NX is designed to support a one way RANlatency of 200 μs.

The application end-to-end delay (defined in 4.2) is most relevant,since this includes the delay caused by core network nodes. Aspectsaffecting the application end-to-end delay are discussed in section3.1.11.

Reliability

The reliability of the connectivity (defined in section 4.3) is theprobability that a message is successfully transmitted to a receiverwithin a specified delay bound. The reliability requirements for C-MTCapplications vary greatly. Requirements on the order of 1-1e-4 aretypical for process automation; requirements of 1-1e-6 are typicallymentioned for automotive applications and automated guided vehicles. Forindustrial automation use cases several sources mention requirements of1-1e-9 but it should be understood that this value comes fromspecifications derived from wired systems and it is unclear if suchstrict requirements apply to systems designed for wireless connectivity.

It is assumed here that most C-MTC applications can be supported with areliability of 1-1e-6 but NX is designed to provide reliability in theorder of 1-1e-9 for extreme applications. The strictest requirement isonly foreseen in localized environments (e.g., a factory) withcontrolled interference levels.

Service Availability

Many services requiring reliable low latency communication also requirehigh service availability (defined in section 4.3). For a certainreliable-low-latency service—e.g., a pair of reliability and latencybound—a service-availability can be defined as to what level thereliability-latency is provided in space and time. This can be enabledby corresponding deployment and redundancy of the network. Architecturalaspects related to service availability are discussed in section 3.1.11.

3.1.3 Numerology and Frame Structure

NX contains several different OFDM subcarrier bandwidths (see Section2.3) spanning the frequency range from sub-1 GHz to 100 GHz, withincreasing subcarrier bandwidth towards higher carrier frequencies.Numerologies with wider subcarrier bandwidths provide, in addition toincreased robustness to Doppler and phase noise, also shorter OFDMsymbol and subframe durations, which provide shorter latencies. As longas the cyclic prefix of the more wideband numerologies is sufficient,these numerologies can also be used at lower frequencies.

In wide-area deployments, numerology “16.875 kHz, normal CP” ispreferably used with a subframe duration of 250 μs. This subframeduration is sufficient for many low-latency applications. For extremedemands on latency, even the numerologies “67.5 kHz, normal CP” or “67.5kHz, long CP b” can be used. If a cyclic prefix of around 0.8 μs issufficient “67.5 kHz, normal CP” should be used due to its lower CPoverhead of 5.5%; for environments with larger delay spreads “67.5 kHz,long CP b” should be used.

In dense macro deployments “67.5 kHz, normal CP” can probably still beused (assuming low delay spread) enabling subframe durations of 62.5 us.If 250 μs is sufficient both “16.875 kHz, normal CP” and “67.5 kHz,normal CP” can be used, provided the frequency range allows for 16.875kHz subcarrier bandwidth.

Even lower subframe durations (7.8 μs) are enabled by numerology “540kHz, normal CP”. Presently, there are no known use cases where such lowsubframe durations are required; furthermore, the small cyclic prefix ofthis numerology (0.1 μs) limits the deployment to very dense ones. Shortsubframe durations would open up the possibility of HARQre-transmissions to increase reliability. However, it is expected thatthe typical operating point for C-MTC is such that code rates above 0.5are used and thus the benefits of re-transmissions are limited.

TABLE 12 Summary of which numerology to choose in which deployment andthe provided subframe duration sub-1 to 6 GHz 6 to 30 GHz 30 to 100 GHz(low frequencies) (medium freq.) (high frequencies) Wide-area 16.875kHz: 67.5 kHz: NA 250 μs 62.5 μs 67.5 kHz: 62.5 μs or 125 μs Small cell16.875 kHz: 67.5 kHz: 540 kHz: 250 μs 62.5 μs 7.8 μs 67.5 kHz: 540 kHz:(very small cells) 62.5 μs 7.8 μs 540 kHz: (very small cells) 7.8 μs(very small cells)

Choosing the right numerology has less impact on the reliabilityrequirements (except that an application should use the correctnumerology with respect to phase noise and maximum expected Dopplershift).

3.1.4 Synchronization in C-MTC

Synchronization plays a critical role when it comes to fulfil the desirein C-MTC for ultra-high reliability.

NX is based on a lean design where the transmission of broadcast signalslike MIB/SIB or similar and synchronization signals are only transmittedwhen necessary. For NX, periodicity of synchronization channels is onthe order of 100 ms. The sparse nature of synchronization signals maybecome critical to achieve the highest detection rates of up to 1-1e-9in some C-MTC scenarios. This is due to the unavoidable time andfrequency drift that occurs due to sparse synchronization signalpattern.

However, it can be shown that with a crystal oscillator (XO) having atime drift of 2 ppm (i.e., 2 μs-per-s) and the maximum frequency driftof 125 Hz/s @2 GHz band, synchronization accuracy is good enough forC-MTC by reusing SS. This applies to both the 16.875 kHz numerology andthe 67.5 kHz numerology.

3.1.5 C-MTC Duplex Mode Implications

Focusing on the strictest reliability cases, with error rates down to 1e-9, the most challenging scenario to fulfill the latency requirementsis for sporadic data where we assume that the UE does not have any ULgrant, and therefore needs to transmit a scheduling request (SR), andreceive a scheduling grant (SG) before commencing uplink transmission.Depending on the duplexing mode used, FDD or TDD, the C-MTC worst caselatency will to some extent vary, as discussed below.

3.1.5.1 FDD

For use cases with the most challenging latency requirements ReferenceSymbols (RS) are transmitted in the first OFDM symbol to enable earlydecoding. In the case that strict processing requirements can be put onUE and eNB (see later section), the respective node's decoding of thescheduling request and grant messages can be made during some few microseconds. Hence, the SR, SG and data can then be transmitted in threeconsecutive sub frames. Then, the worst case scenario is when the datato transmit arrives right after a sub frame have started, and hence thetotal RAN latency will be between 3 subframes (best case) and 4 subframes (worst case). See the illustration of UL latency with SR-SG-Datacycle for FDD shown in FIG. 69. As seen in the figure, the ReferenceSymbol (RS) is transmitted in the first OFDM symbol in each sub frame(assuming 1 subframe=4 OFDM symbols, as in section 2.3.2.1) for enablingearly decoding. Given the use of the 67.5 kHz numerology with a subframelength of 62.5 μs, this implies a RAN latency of around 187-250 μs. Itis assumed here that the data is coded at sufficiently low rate so thatno retransmission is needed.

So, from a latency perspective, using FDD is a good solution infrequency bands where FDD is available (e.g., sub 4 GHz).

Note that FIG. 69 shows the UL latencies assuming that the PDCCH isspread over the whole subframe consisting of 4 OFDM symbols (see section2.3.3). Note that where PDCCH is limited to the first symbol of asubframe, to allow early decoding, the total UL delay can further bereduced to 2 subframes (in best case), since the PDCCH is limited to thefirst OFDM symbol of the subframe allowing the transmission of data inthe same subframe. This RAN latency should be seen as a technicallychallenging feature of NX as it requires that strict processingrequirements can be put on UE and eNB. In other words, the SG needs tobe processed in around 8 μs (less than OFDM symbol duration of 67.5 kHznumerology) as described in further sections below, requires premiumdevices and may not be achievable in MBB devices. Resulting delay formore relaxed processing times are presented in section 3.1.12.

3.1.5.2 TDD

Below is described the latency for a TDD configuration. The analysistakes into account the high reliability requirements of challengingC-MTC use cases. Hence, the analysis should be seen as a worst caseanalysis and in many scenarios (but probably not all) one probably canrelax requirements like synchronized cells, etc. In TDD, the delayrequirements may imply significant restriction on the TDD UL/DLstructure. Again focusing on the worst case scenario with no UL grantfor a UE and 67.5 kHz numerology, one can easily conclude that the UL/DLsubframes need to alternate on single sub frame basis, and hence underthese circumstances dynamic TDD could not be used. Then, the worst casedelay is when data arrives at beginning of an UL sub frame. Again it isimportant to note that in cellular TDD, one can typically not start anUL transmission in a subframe where nearby C-MTC UE has DL reception.Therefore, the UE has to wait for next available UL subframe for the SRtransmission. Then the total delay is 5 sub frames, 312 μs. The bestcase delay is when data packet arrives prior to next UL sub framesimilar to the best case FDD, 187 μs. This is shown in FIG. 70, whichillustrates latency for TDD. In this worst case example, a data packetarrives at the UE in beginning of a UL sub frame and therefore SR (firstarrow) could be transmitted first in next available UL sub frame. ThenSG and Data can be transmitted in forthcoming sub frames.

In TDD, time needs to be allocated for the UE to change transceiversettings between UL and DL. The need for alternating UL/DL on single subframe basis may then imply a significant overhead in switching. However,by using the timing advance the overhead can be restricted to 1 UL OFDMsymbol. This is shown in FIG. 71, which illustrates switching overheadand demonstrates that using TA, the switching time can be reduced to oneUL OFDM symbol. Using that approach, around 8 μs for switching can beallowed, which is sufficient looking at current implementationsrequiring some 5-6 μs,

3.1.5.2.1 Implication of Worst Case C-MTC Requirements on TDD

The need for alternating between UL and DL for every sub frame implies a25% capacity loss on the UL channel. Taking into account the “TDD 100 dBdynamic near-far problem” in a cellular deployment scenario togetherwith the high reliability requirement for C-MTC, both intra andinter-frequency adjacent cells need to be synced and have the same UL/DLconfiguration. This might not be optimal from a Mobile Broadbandcapacity perspective point of view. Another approach is to only deploythe C-MTC applications with the toughest requirements (requiring down to1 e-9 error rate) in isolated cells or areas.

3.1.5.3 A Note on Processing Time

In order to be able to fulfill the short processing times needed forresponses in adjacent subframes, different pre-processing principles canbe used using the fact that the data packet transmitted in C-MTC islikely to be small as well as only a small finite set of packet sizesare allowed (only a finite set of messages to be transmitted with suchstrict latency requirements). Assume that the eNB as well as the UE hascontrol of the current link quality and hence know what MCS to use, andonly a small number (single) of MCS formats for a given data packet sizeis possible to choose for the NW node. Then, once the UE transmits a SR,it includes the data packet size in the message. Furthermore, the UE canprepare a finite set of possible MCS formats and once the SG is decoded(indicating which f/t resources to use), the UE can transmit the correctversion in these resources without further coding delay. The same can bedone in eNB. Once the SR is received it allocates the resources neededbased on data packet size information and already determined MCS andtransmits the corresponding SG. Using this kind of preparing/pre-codingapproaches we expect that one can fulfill the coding and decoding timerequirements needed for the C-MTC timing constraints.

3.1.6 Coding and Modulation

C-MTC applications need robust modulation and coding as well as fastdecoding to fulfill the latency requirements. In order to achieve thelatency for the most demanding use cases, C-MTC applications may have todisable HARQ and use very robust MCSs. Hence modulation order shouldpreferably be low (e.g., QPSK). Furthermore, coding strategies allowingearly decoding are desirable, hence convolution codes withoutinterleaving might be a good choice not only from the early decodingpossibilities but also as C-MTC packets are expected to be small, andhence the gain of using advanced coding principles, are limited (polarcodes, which are currently the preferred approach to MBB in NX, may alsobe applicable for C-MTC). Another important enabler for fast and earlydecoding is to put reference symbols in the beginning of the subframe inorder to be able to do channel estimation without buffering.

For less extreme reliability and delay requirements, it is likely thathigher order modulation is beneficial.

3.1.7 Diversity

Diversity is considered to be an important enabler of ultra-reliablecommunications. Large diversity orders (e.g., 8 or 16 for the strictestreliability requirements up to 1-1e-9) are desirable to allow acceptablefading margins in case of fading channels, such as Rayleigh channel.Theoretically, this diversity could be achieved in the time, frequency,and/or space domain. In order to achieve ultra-reliable communicationwithin the strict low latency budget, exploiting the time diversity isvery challenging. On the other hand, to exploit the gains from frequencydiversity, it is important to map the coded bits on the frequencyresources having uncorrelated channel coefficients. Therefore, therequired bandwidth would increase with the coherence bandwidth of thechannel and thus make the exploitation of frequency diversity morebandwidth consuming. Therefore, antenna diversity is assumed to be themain option to achieve the required diversity order where feasible. Itis also to be noted that in order to have a spatial diversity order of16, 8 and 2 antennas could be considered at eNB and UE side,respectively. In device-to-device (D2D) transmission, it may not befeasible to achieve sufficient diversity gains with only spatialdiversity due to limitations in the antenna design for the UE, frequencydiversity could be used on top of it. In addition, D2D communicationalso benefit from increased link budget due to proximity of devices.Moreover, to harvest the full transmit diversity gains, more advancedspace-time codes need to be used rather than the Alamouti-code.Alamouti-codes achieve full transmit diversity only up to 2 transmitantennas.

An extension of antenna diversity is macro-diversity, where antennas arenot co-located but distributed in space. This requires fast connectivitybetween different reception points if delay is critical. In a moregeneral case, one can consider serving applications with high demands onreliability over multiple carriers or even RATs.

Diversity for data and control channels is further discussed in sections2.3.3.2, 2.3.4.1, and 2.3.5.1.

3.1.8 HARQ

For the most latency sensitive C-MTC services, it is expected that thelatency requirements prohibit the use of HARQ, and that successfuldecoding is required in a single transmission attempt. Accordingly, theHARQ functionality may be disabled for such applications. For serviceswhere HARQ feedback would be possible from a latency perspective, thegains from HARQ are still limited. Since many C-MTC services have nointerest in “average latency,” but only the latency at a givenpercentile, link adaptation needs to ensure reliability is met after themaximum number of retransmissions allowed by the latency budget. Thismay often end up being a format that is hard to decode earlier; for goodSINR there is little motivation to use code rates below ½, meaning thatdecoding is possible first after half the transmission.

The potential gains with HARQ depend also on whether SINR can be adaptedby changing transmission bandwidth. For uplink, only limited gains areexpected if the bandwidth can be reduced, and with that the SINRimproved. However, for downlink or uplink cases where there arelimitations on the power spectral density, where the code rate needed tomeet the error-target is very low, significant resource efficiency gainscan be expected from HARQ operation. To benefit from the reduced averageresource utilization, scheduling needs to be sufficiently fast toutilize the “freed up” resources for other services.

It is recognized that the HARQ feedback also need to be robust forNACK-to-ACK errors down to the given reliability target, and even lowerfor multiple transmissions and it also needs to meet this reliability ata significantly lower latency bound than for the application itself.This can challenge the coverage of HARQ feedback and make it costly,especially considering relatively small expected data sizes for C-MTC.The HARQ mechanism and considerations of the control channels arediscussed in section 2.2.8.

FIG. 72 illustrates an example where the fast HARQ feedback istransmitted at the end of the first available UL transmission occasion.In this example HARQ feedback is included in a single OFDM symbol.

It is expected that only the “very fast HARQ feedback” option in NXwould be applicable for C-MTC, with significant energy allocation to thefeedback to meet error requirements without having to set detectionthresholds so that all HARQ gains are lost to ACK-to-NACK errors. With“very fast” feedback, where the feedback channel only spans a fractionof a subframe the round-trip time is expected to be 2 subframes, where atransmission can occur in every other subframe with stop-and-wait. For“early termination,” continued transmission until ACK, one subframe willoften be “lost”. If predictive feedback is supported based on qualityestimation on early pilots the feedback could even be sent beforecomplete decoding. This scheme may not be suitable in case of verystrict reliability requirements.

3.1.9 MAC Access Schemes for C-MTC

NX C-MTC MAC design is based on the L2 design principles as described inSection 2.2.1, and exploits the NX PHY framework. Several C-MTC MACoptions, which could be selected flexibly depending upon the scenario,are described here. The design modularity provides the possibility toplug-in different MAC components and functionalities in order to moreaddress specific use-case requirements. In order to meet the desired QoSdemands such as the latency bounds and reliability requirements, each ofthe C-MTC MAC options has its characteristics and tradeoffs in terms ofresource requirements and resource utilization.

In particular, the C-MTC MAC design includes (i) dynamic scheduling,(ii) instant uplink access and (iii) flexible contention-based access(hybrid access) schemes. MAC schemes for C-MTC in D2D have so far notbeen studied explicitly. Dynamic scheduling is considered as a baselinecase, where the benefits of NX PHY (e.g., shorter and variable TTIs) canbe exploited for fulfilling low latency and high reliability demands.The dynamic scheduling option suits to sporadic data traffic, wheregrant to resources is given by a base-station upon scheduling requestfrom a node for a single transmission. For each required datatransmission, the resource grant needs to be obtained from thebase-station. Depending on the scenario-specific QoS expectations andavailability of resources, a base-station has the possibility toprioritize sporadic real-time data over other traffic types.

The Instant Uplink Access (IUA) scheme uses over-provisioning ofresources for uplink data transmission. This MAC option sacrificesresource utilization in favor of latency reduction, which is desirablefor C-MTC applications. Since a node does not need to explicitly obtaina grant from the base-station for an upcoming sporadic datatransmission, IUA eliminates the delay involved in the cycle ofrequesting for a resource and the base-station assigning the resource.The hybrid access scheme uses both scheduled and contention-based accessprinciples, and is designed to exploit the flexibility in selecting theresources and frame structures offered by NX PHY. In the hybrid accessscheme, the base-station reserves prior resources for periodic real-timeand non-real-time traffic. Moreover, depending upon the availability ofresources and expected sporadic traffic at a given time, thebase-station can flexibly assign both contention-based and scheduledresources to nodes. The base-station can even re-configure the assignedresources when required, e.g., take away assigned resources tonon-real-time traffic and reserve them for real-time traffic. If thetraffic load is low, contention-based access can be fairly efficient interms of resource utilization efficiency, and thus can efficientlyhandle sporadic traffic. However, contention-based access has thedownside of its non-deterministic behavior. Therefore, in this MACoption, the base-station needs to manage radio resources forcontention-based and scheduled access in a way that real-time trafficrequirements of very low latency and high reliability can be satisfied.The above mentioned C-MTC MAC schemes are described in Section 2.2.9.

3.1.10 D2D Aspects

Device-to-Device (D2D) communication protocols for NX (see section 3.11for further details) are designed to support proximal communications inin-coverage, partial coverage and out-of-coverage scenarios for a largevariety of use-cases, including mobile broadband, as well asmission-critical use-cases such as V2X and factory automation.

For the mission-critical use cases, the application requirementsassociated with reliability, availability and latency may be more easilymet by taking advantage of direct D2D communication than without D2Dcapability. This is because in case of infrastructure-basedcommunication, every data packet between devices, even if the devicesare in each other's proximity, is involved in one UL and one DLtransmission. This may not always be the optimal path in terms oflatency compared to a single radio transmission along the direct pathbetween the nearby devices. Furthermore, network coverage or capacitymay not always be guaranteed for the mission-critical communications.Therefore, sidelink integration may help network provide higheravailability by avoiding potential dimensioning bottlenecks where theinfrastructure may become a single point of performance degradation or apotential failure. Note that the reliability gain with D2D due to fewercommunication links may be partly offset by lower diversity order forthe sidelink.

Some C-MTC applications need to be operated in out-of-coveragescenarios, e.g., some automotive scenarios. Then, D2D communication maybe the only path seamlessly available in both in-coverage andout-of-coverage situations.

In case of in-coverage scenarios (e.g., factory automation),network-assistance for D2D plays an important role to reduceinterference between devices and infrastructure; as well as to improvethe spectral efficiency by enabling the reuse of resources. Furthermore,the network can further assist the devices for device discovery andmobility.

To realize the potential latency gains by means of direct D2Dcommunications, RRM functions (see section 3.11.7.8 for furtherdetails), are provided in a hybrid centralized-distributed fashionbetween the network and the devices depending on the scenario andservice. These RRM functions may include mode selection, resourceallocation and power control, and jointly ensure that radio resourcesare made available for coverage extension as well as mission criticalservices.

To have robust transmissions against unexpected interference in case ofdistributed RRM, reliable channel codes with low-error floor (e.g.,convolutional codes) may be used. Smart retransmission mechanisms (e.g.,HARQ), may be used if it is possible to do retransmissions within thelatency bound.

To further protect the sidelink transmissions from interference, boththe network-assisted (slow) and non-assisted (fast) RRM procedures needto be implemented with robust interference management and co-ordinationmechanisms for the unicast, multicast and broadcast D2D communicationchannels.

To cope with the dynamic radio network environment due to mobility,diversity could be an important aspect for mission-criticalcommunications, which can be provided in different forms such asantenna-diversity, frequency-diversity, time-diversity (see section3.1.7), and, in case of D2D, also in mode-diversity (involving cellularmode and D2D mode for proximal communications). On the other hand, thesediversity methods may not always be available:

-   -   The latency requirement may be a limiting factor to utilize        time-diversity.    -   The frequency diversity could be limited due to frequency        allocation and radio capabilities.    -   D2D links may be restricted to lower diversity order due to the        fact that typically a smaller number of antennas are available        at a device compared to a network node.    -   Depending on the network coverage, the mode diversity, where        both infrastructure-based (Uu interfaces) and D2D (PC5        interface) connectivity can be used, may be limited to the        control plane or not available at all.

All in all, NX D2D is seen as a complementary enabler for low latencywhen the right tools are used, thanks to shorter communication distance,fewer transmission links (hops), as well as high reliability by means ofenhanced Layer 1 and Layer 2 functionalities e.g., for redundancy,interference management and coverage extension.

3.1.11 RAN Architecture Aspects

This section describes architectural aspects related to achieving lowlatency, high reliability and high availability on a system level.

Need to Support Distributed Functionality:

In order to support e2e latencies down to 1 ms or below, it is requiredto support deployment of application servers close to the radio access,sometimes referred to as mobile edge computing. Light in an opticalfiber travels around 200 km in 1 ms so in order to achieve guaranteedone-way latency between say a controller in the network and a wirelessactuator/sensor, the controller application needs to be located muchcloser to the radio than 200 km (also taking into account additionaldelays coming from switching, HW-i/f, fiber not deployed in a straightline, etc.). Deploying the application servers close to the radio alsomeans deploying the core network user plane functions such as mobilityanchoring close to the radio.

For the low latency and high reliability use cases, it is interesting tobe able to deploy both user plane and control plane functions close tothe radio network. The distributed user plane functions are motivated bythe need for low latency, while the distributed control plane functionscould be motivated by the need for stand-alone operation even if theconnection to external networks is broken.

Using Distributed Cloud and Network Feature Virtualization (NFV) toDistribute Functionality:

In the 2020 time-frame, it is expected that future core networkfunctions as well as most application level functions will be supportedon general purpose processing HW and be deployed as virtualized networkfunctions. Virtualization makes it easy to distribute these functionsout in the network using a distributed cloud platform based on generalpurpose HW. NX supports such distribution of both core network andservice layer (e.g., application services) functionality, which enableslow latency connections between sensors, actuators and controllers.

It is also possible to support critical and low latency services in aseparate logical e2e network slice, (see section 1.1 for a descriptionof network slicing), which is optimized for reliable and low latencyservice (e.g., support distributed functions). This network slice sharesthe same physical network as say a MBB slice, but can still be betterthan the MBB to handle critical traffic. In this case, mechanisms needto be in place that handle the sharing of resources between slices andprovide isolation. In many cases, network slicing is envisioned to usedynamically shared resource, but for critical slices it would also berequired to assign some guaranteed (dedicated) transport network andradio resources to the slice to make sure that the performancerequirement can be met.

Architecture Enablers for Achieving High Level ofReliability/Availability:

In addition to requirements on high reliability, some services require ahigh service availability even at times of node or equipment failure.Today typical critical MTC applications utilize two independentduplicated paths to ensure that the overall connection can cope with aHW or SW failure in one path. It is expected that similar concepts canbe applied for critical MTC using NX.

FIG. 73 illustrates the use of duplicate paths.

In addition to independent duplicated paths it is possible to achievehigh node availability by replicating the UE context in multiple nodesto cope with HW boards failing or VM failures. Such methods are alreadyin use today in our products.

3.1.12 Achievable Latency

The achievable RAN latency is summarized in this section. This sectionfocuses on FDD which gives the lowest latency as discussed in previoussections. It should be noted that the end-to-end or application latencyis longer and includes buffering, transport delay and processing delayin core network nodes.

3.1.12.1 Uplink Latency

The achievable uplink user plane latency for NX is shown for scheduledtransmission in this section. With an aggressive assumption onprocessing time (8 μs) it is possible to transmit scheduling request(SR), scheduling grant (SG) and data in consecutive time slots. This canbe seen as the technology potential for premium devices with strictlatency requirements and is in line with the numbers described in insection 2.1.5.1. With a more relaxed assumption on the processingrequirement (several tens of μs) there is a one-subframe delay until thefollowing message in the sequence is transmitted. The exact processingtime is then not important as long as it does not exceed one subframe.This is assumed to be possible also for mainstream MBB devices.

The steps involved and the latency required for each step can be seen inFIG. 74, which shows uplink RAN latency for dynamic scheduling. When noretransmissions are used, the resulting latency is 4 subframes forstrict processing requirements and 6 subframes for relaxed processingrequirements.

When HARQ retransmissions are used, each retransmission adds anadditional 2 subframes (strict processing requirements) or 4 subframes(relaxed processing requirements).

The schemes Semi Persistent Scheduling, Instant Uplink Access andPredictive Prescheduling result in very similar latency. In all theseschemes, the scheduling request-grant cycle is omitted and a schedulinggrant is available when data arrives. Details of these schemes are givenin section 2.2.9. The steps involved and the latency required for eachstep can be seen in FIG. 75, which shows achievable uplink latency withInstant Uplink Access. When no retransmissions are used, the resultinglatency is 2 sub frames both for strict and relaxed processingrequirements. When HARQ retransmissions are used, each retransmissionadds an additional 2 subframes (strict processing requirements) or 4subframes (relaxed processing requirements).

The resulting uplink air interface latency for different numerologiesand scheduling schemes is summarized in Table 13.

TABLE 13 Summary of achievable uplink RAN latency for differentnumerologies Sub frame Scheduling Optimal Relaxed duration OptionProcessing Processing 250 us Dynamic 1 ms 1.5 ms 250 us Instant UplinkAccess 0.5 ms 0.5 ms 62.5 us  Dynamic 0.25 ms 0.375 ms 62.5 us  InstantUplink Access 0.125 ms 0.125 ms

As can be seen, the one-way air interface latency target of 200 μs canbe reached in uplink with the appropriate configuration.

3.1.12.2 Downlink Latency

For low latency communication it is possible to send a schedulingassignment for downlink data and the data transmission in the samesubframe. The scheduling assignment is transmitted on the PhysicalDownlink Control Channel (PDCCH) in the beginning of a subframe and thedata transmission can be done in the same subframe; see section 2.3.2.2.

When data is available for downlink transmission, the data can betransmitted in the next available subframe. This means that the worstcase for the RAN latency in downlink is limited 2 subframes (500 μs for250 μs subframe duration and 125 μs for 62.5 μs duration). The latencyrequirement of 200 μs can thus be met.

In a product implementation it is possible that 1-2 subframes need to beadded for scheduling, link adaptation and processing, meaning that thestrictest latency requirements may not be reached unless an optimizedimplementation is used.

3.2 System Access

This section describes functionality provided for users to access andproperly operate in the system. The functionality provided to users mayinclude one or more of:

-   -   Providing devices with “system information”—In LTE networks,        typically done by means of per-cell broadcast    -   Paging—In LTE networks, typically done by means of per-cell        broadcast over a multi-cell paging area    -   Connection establishment—In LTE networks, typically targeting a        certain cell    -   Tracking—In LTE networks, typically handled by cell selection        and reselection

The term system access in this section refers to all signals andprocedures enabling the UEs to access the system and to receive paging.In this section, the properties and solutions that are relevant forsystem access in NX are described.

In 3G and 4G systems, the transmission of these system access relatedsignals are the main contributor to network energy consumption. Thereare two parameters that impact the network energy consumption more thanany other: the amount of discontinuous transmission (DTX) (the maximumDTX ratio) that can be enabled and; the length of the discontinuoustransmission intervals (the maximum sleep duration) that is supported.For NX, the system access functionalities are designed such that theDTX-ratio and the sleep duration of the network nodes are sufficientlylarge. In general, this could be interpreted as “the more DTX thebetter”. But in practice, each node has some user-plane traffic also. Ina typical node in LTE networks, active mode transmissions occur lessthan 10% of the time and if the mandatory transmissions are sufficientlybelow that, say 1% of the time, not much is gained by increasing the DTXratio further.

In legacy systems, the interference caused by system access relatedsignals significantly reduces the peak user data rates. In particular,at low system load the interference is dominated by the mandatory systemtransmissions (CRS-based signals in LTE) and thus limits the SINR.

System access related signals need to be omnipresent and static. It isnot acceptable that a certain location has system coverage onlysporadically, depending on how the system is currently configured. Inlegacy systems, this has often proved to be an obstacle to the use ofdynamic optimization involving re-configurable antennas.

Since NX is based on supporting dynamic massive beamforming, NX isdesigned such that there is no coupling between the normal user- andcontrol plane related signals and procedures and the system accessrelated signals and procedures. Such a de-coupling is an importantenabler for full dynamic optimization of the user-plane andcontrol-plane signals related to a single UE.

In order to comply with the ultra-lean design principle of NX it isimportant that the NX system access functionality is as lightweight aspossible, while ensuring reliable and fast access. Note that the factthat the system design is lean and supports long network DTX durationsdoes not directly imply any additional access delay. If, for example, adownlink signal is transmitted every 100 ms or every 5 ms, the systemcan still be configured with a random access opportunity, e.g., every 10ms, in which case the initial access delay would be the same.

3.2.1 Design Targets

The following subsections list some of the design targets considered forthe system access.

3.2.1.1 Scalability

NX is designed to ensure that different parts of the system scaleindependently. For example, there should be no need to add morecommon-signals when densifying networks. In other words, it is possibleto densify only the data plane and not the system access relatedoverhead. The reason for densifying the network is most often a lack ofcapacity and not because random access or paging performance is notsatisfactory, for example.

Furthermore, different sectors or beams associated with the same networknode shall be able to share system access related functionalities suchas system information. Also, CoMP clusters or C-RAN implementationsinvolving several network nodes or antenna locations shall be able touse one single system access configuration that enables system accessand paging functionality to the entire cluster. For example, if a groupof nodes share the same system access configuration then a separatelayer can be used for system access (possibly on a lower frequency).

It shall also be possible to have only one system access configurationfor an entire network layer such that idle mode UEs only know how toaccess that layer without necessarily being aware of which node in thelayer will respond to the network access.

Nodes that are added where system access functionality is alreadyadequately provided can operate without transmitting any system accessrelated signals. When adding additional frequency bands to an existingnode, transmission of system access related signals on those frequencybands shall be optional.

The system access design shall support that system information broadcastmay be transmitted using broadcasting transmission formats such assingle-frequency network (SFN) modulation. It shall also be supported totransmit system information to the mobile terminals in a dedicatedtransmission format when that is more efficient. The amount of systeminformation that is constantly broadcasted over the whole coverage areashall be minimized and primarily related to enabling initial systemaccess.

3.2.1.2 Deployment Flexibility

The system should allow for massive deployment of low-power access nodeswithout excessive overhead cost. In very dense deployments supportingvery high data rates (e.g., by means of large bandwidth and/or a largenumber of antenna elements), the individual nodes have no data totransmit or receive most of the time. Therefore, when calculating theoverhead cost of the system access functionality it is important to notonly use a fully loaded system as a reference, but also to calculate theoverhead cost in a completely empty network.

3.2.1.3 Flexible to Allow for Future Radio-Access Evolution(Future-Proofness)

The initial discussions in 3GPP about 5G standardization currentlyassumed a standardization process in phases where the first release maynot address all envisioned features and services. In other words, thenew 5G air interface to be standardized in the initial release wouldneed to be prepared for the introduction of new features and networkfunctions that is difficult to predict what they are going to be sincethere could also be new requirements that are not yet being considered.

Some level of future-proofness has been already achieved in the LTEdesign, which can be acknowledged by the large amount of new featuresthat were introduced, e.g., eICIC, CoMP, UE specific DMRS, relaying, MTCenhancements (incl. Cat 1/0), LAA, Wi-Fi integration, carrieraggregation, and dual connectivity, while still supporting multiplexingwith legacy Rel-8 UEs. In addition to these features, 3GPP has managedto introduce new services to the LTE air interface, such as mMTC and V2Xcommunication. During this process of introducing new features andservices some lessons have been learnt and these have driven designprinciples to make the new 5G air interface even more future proof thanLTE. Some of these principles, such as ultra-lean design andself-contained transmissions, have an important impact on the way systemaccess (and mobility) procedures are designed since some of the commonsignals/channels used are broadcasted.

3.2.1.4 Enabling Superior Network Energy Performance.

Using the EARTH energy efficiency evaluation framework (E³F) we obtainthe results in FIG. 76, which shows the empty sub-frame ratio andnetwork area power usage in a typical European nationwide network,according to several scenarios detailed below:

-   -   Scenario 1: “the most relevant traffic scenario for 2015”    -   Scenario 2: “an upper bound on the anticipated traffic for 2015”    -   Scenario 3: “an extremity for very high data usage in future        networks”

For a nation-wide network, the energy usage when averaged over 24 hoursis almost independent of the traffic. Note that these results do notassume any densification of the network, so it is very unlikely that therelatively high dynamic energy part of 7.4% for Scenario 3 will beobserved in a future network. Even though traffic is expected toincrease significantly in the future the energy usage in legacy systemswill still depend very little on the actual traffic in the network.There is a large potential to reduce the 5G energy consumption bydesigning a solution with lower static power consumption.

3.2.1.5 Enhanced Support for Massive Beamforming

Another topic considered when designing the NX system access functionswas the recent developments in the area of advanced antenna systems andmassive MIMO. As a comparison, the LTE-standard defines mandatorytransmissions of cell-specific reference signals (CRS), primary andsecondary synchronization signals (PSS and SSS) and physical broadcastchannel (PBCH), and system information blocks (SIBs) via the downlinkcontrol and shared data channels (PDCCH and PDSCH). Looking at an“empty” LTE radio frame with no data it is evident that a large numberof resource elements are used for these system level functions.

In previous cellular systems, there was an underlying assumption thatcells are static and that they do not change their shape. This is aproblem for the introduction of advanced and re-configurable antennasystems in these networks, since even such simple things as adjustingthe tilt of an antenna cannot be done without affecting the coveragearea of the network. The tight interconnect between system-accessfunctions (such as random access and paging) and user- and control-planefunctions is very often an obstacle for introducing any kind of fastantenna configurability in the network. Therefore, the usage ofre-configurable antenna systems (RAS) in conventional networks is verylimited.

Requiring mobile terminals to receive system access related signals andnormal data- and control-plane related signals at the same time, on thesame carrier, puts very high requirements on dynamic range in the UEreceivers. System access related signals need to cover the whole area,while UE-specific signals may have a significant link-budget gain frombeamforming. Thus, a power difference of 20 dB or more between these twokinds of signals is likely in some scenarios. Therefore, in NX themobile terminals shall not be required to listen to system-accessrelated signals at the same time as they receive data- and control-planerelated transmissions from the network.

These targets should be balanced with the fact that it is beneficial tohave harmonized solutions for both high frequency and low frequencybands so that the different bands are not like different systems from alower layer perspective.

3.2.2 System Information Acquisition

A set of requirements on system information distribution is given insection 2.1.6.1. One way to address these and the design target toenhance the support massive beamforming is to reduce broadcastedinformation in the system to a bare minimum. One approach is tobroadcast only enough information that UEs need to send the initialrandom access to access the system, in the following referred to asaccess information. All other system information can be delivered to theUE using dedicated transmission with high-gain beamforming, or it can bebroadcasted upon request by at least one UE. An extreme is to hard codea default configuration of the access information in the specification,in which case no broadcast of access information may be needed. Therequest could be sent using a default set of access parameters.

3.2.2.1 Contents of Access Information

The design builds on the possibility to provide the main part of the NXsystem information on a per-need basis, allowing the reduction of theamount of always-broadcasted system information, and only includinginformation needed to access the system, with node-specific and commonsystem information delivered by dedicated transmission to the UE. Thisis shown in FIG. 77, which illustrates access information distribution.

The access information includes the random access parameters. Theseparameters include selected parts of the MIB, SIB1 and SIB2 informationelements defined in LTE (e.g., PLMN Id, CSG, Q-RxLevelMin,Frequencybandindicator and Prach-configCommon). The exact content of theaccess information may depend on the effects of network slicing.

3.2.2.2 Index Based Access Information Distribution

A technique for minimizing broadcasted information provides a two-stepmechanism for transmitting the access information, comprising an AccessInformation Table (AIT), containing a list of access informationconfigurations and a short System Signature Index (SSI) which providesan index pointing to a certain configuration in the AIT, defining theaccess information. This is shown in FIG. 78, which illustrate AccessInformation Table (AIT) and system signature index (SSI) transmissions.

The content of the AIT is assumed to be known by the UE when performinga random access attempt. The AIT in the UE can be updated in one or bothof two ways:

-   -   A Common AIT (C-AIT) is broadcasted by the network, typically        with a longer periodicity than the SSI e.g., every 500 ms or so.        In some deployments the C-AIT periodicity may be the same as the        SSI periodicity (e.g., in small indoor networks) and the maximum        C-AIT periodicity may be very large e.g., 10 seconds in order to        support extremely power limited scenarios (e.g., off-grid solar        powered base stations).    -   A Dedicated AIT (D-AIT) transmitted to the UE using dedicated        signaling in a dedicated beam after initial system access. The        UE specific D-AIT may use the same SSIs to point to different        configurations for different UEs. For instance, in the case of        system congestion, this would allow to have different access        persistency values for different UEs.

The SSI period is typically shorter than that of the C-AIT. The value isa tradeoff between system energy performance, UE energy performance (seesection 2.1), and access latency in the event that SSI needs to be readbefore access.

3.2.2.2.1 Contents of the AIT

One benefit with the SSI&AIT concept is that the frequently transmittedSSI of limited size can be used to indicate the access information,signaled by C-AIT less frequently. C-AIT can also be transmitted onanother carrier or received via LTE. This separation of the signalsallows broadcasting the C-AIT on a longer time periodicity. However, thelength of the SSI depends on the different Information Elements (IE) ofthe AIT and the number of needed SSI values to point out the differentconfigurations. The gain is expected to be high if the AIT contains onlya few IEs that are dynamically changing, with most values being static.On the other hand, if a majority of the IEs are changing dynamically,the size of the SSI grows, and the expected gain is less. This should beconsidered when selecting which IEs to include in the C-AIT.

An example of possible content of the AIT is illustrated in Table 14,where various combinations of such as basic system information and therandom access related information elements are identified by theSignature Sequence Indices (SSIs). In this example, there is a headersection of the AIT including also the Global time and PLMN Id. However,depending on the coverage of the AIT (see section 2.2.2.2.2) and thelevel of synchronization in the network, it may also be desirable togive additional SFN/timing information from each node to be accessed.

Depending on the number of SSI entries in the AIT, there is potentiallya large degree of repetition in the content, and therefore compressionof the AIT may be used to reduce the size of the signaled information.Current expectations are that a signaled size of 100-200 bits issufficient for the AIT. The physical format of AIT is presented insection 2.3.

TABLE 14 Example of AIT content. Global time PLMN identity list SSI kCSG = 0, Q-RxLevelMin = 12, Frequencybandindicator = 3, Barring info =120, Prach- configCommon = 34 SSI n CSG = 0, Q-RxLevelMin = 14,Frequencybandindicator = 4, Barring info = 48, Prach- configCommon = 20. . . . . .

3.2.2.2.2 Delivery Options of C-AIT

The default delivery option for C-AIT is self-contained transmission inwhich all nodes transmit both C-AIT and SSI, with C-AIT entriesreferring only to themselves. However, there could be heavy interferencefor C-AIT reception within a synchronized network on the same frequency.To avoid C-AIT interference, C-AIT can be time-shifted in differentnetworks. In addition to self-contained transmission, in order tosupport the design target on deployment flexibility, further deliveryoptions for the C-AIT are possible. Some examples of AIT transmissionmethods are listed below, and illustrated in FIG. 79.

One overlaid node can be selected to distribute C-AIT, including theentries of all covered network nodes. Note that the same SSI entry maybe included in neighboring C-AITs, containing the access information ofnodes on the C-AIT border. SSI reuse planning is required to avoidconfusion. The UE derives the timing, demodulation reference signal, andthe scrambling required for receiving the AIT based on the SSIreception.

The payload size of C-AIT can be larger in the self-contained case sinceinformation of all nodes in the coverage area is included in the C-AIT.The coverage is limited by the selected node. It could be applicable fora scenario where C-AIT is transmitted at low frequencies with goodcoverage, to limit the need for broadcast transmissions from highfrequency nodes within this coverage, which would only need to send theshorter SSI (and possibly a small AIT containing only a pointer to theAIT on the lower frequency band).

In the SFN transmission, the nodes in an area, which could be defined as‘C-AIT region’, transmit the same C-AIT, including the number of entriesof this area. Interference is reduced enabling higher spectralefficiency and coverage. In dense areas this SFN can be very large, andeven in very large deployments this gives at least 4 dB additional SINRcompared to sending separate Ails from each node.

In the case of LTE-NX tight integration, the C-AIT could also bedelivered by LTE. It is also possible to hard code a few sets of defaultaccess parameters with corresponding SSIs in the 3GPP specificationwhich are then universally applicable for UEs detecting such SSI. Inthis case C-AIT acquisition is not needed, and after initial systemaccess, the UE can be provided with a D-AIT over dedicated signaling.

3.2.2.2.3 SSI Structure

The SSI contains a bit sequence, containing a pointer into the AIT andalso a version indicator of the AIT. This pointer may be understood asan uplink access configuration index, as it is used as an index to theAIT, to obtain the appropriate uplink access configuration. The versionindicator enables the UEs to verify that the AIT has not changed andthat the related access information is still valid. The SSI may alsoprovide information related to the demodulation and descrambling of theC-AIT.

3.2.2.2.4 SSI Block (SSB)

To support delivery of a payload of necessary information bits, an SSIBlock (SSB) could be introduced and transmitted from nodes nottransmitting the C-AIT and always follows a normal SSI transmission. Thecontent in this block could be flexible to take the system information,which needs the same periodicity as SSI, such as “an AIT pointer” and“SSI payload”. The AIT pointer is denoted as to indicate the time andband where the terminals can find the C-AIT and even the transmissionformat to avoid full blind detection. The SSI payload can be denoted asto deliver more bits than the sequences can, the SSI can be transmittedas a codeword in the block. Note that the other system information thatis not feasible or sensible to include in the AIT could be also involvedin the block, e.g., additional timing information for UEs waking upafter long DRX (see section 2.2.4.3).

3.2.2.2.5 AIT Information Update

Different mechanisms can be used to ensure UEs always have an up to dateAIT. Some alternatives are listed below on how AIT validity can bechecked by the UE:

-   -   UE detects an SSI which is not included in its AIT    -   UE detects a change in the SSI version indicator    -   There can be a validity timer associated with the AIT    -   The network can signal AIT update through paging indication

There may also be a need for the network to check that the UE has an upto date AIT. This could in turn be enabled by

-   -   The UE calculating a checksum of its AIT and sending it to the        network. The network checking the checksum to determine whether        AIT update is needed.

The network may also store and maintain a mapping between different AITcheck-sums and AIT content such that it is possible to retrieve an AITthat a UE is configured with based on receiving only the check-sum fromthe UE.

3.2.2.2.6 UE Procedure

There are different L1 procedures for different UEs with differentknowledge level on AIT, as illustrated in FIG. 80. The UEs without AITwould start the access procedure to obtain the periodical AIT to detectthe PACH, as described in section 2.3, using the self-containedreference signals. Once having the AIT, the UEs can do initial accessprocedure after detecting the Signature Sequence (SS), which is mappedfrom the higher layer SSI as also described in Section 2.3.4.1. Therelevant information for the initial random access is obtained from theAIT according to the SSI.

The initial random access procedure for a UE, with or without AIT, fromthe L1 aspect is shown in FIG. 81. The UE always scans SSIs to knowabout the serving coverage after power-up. Once detecting SSIs, the UEchecks local AIT, e.g., determining whether or not any of them is in thetable. In this step, the receiving power and synchronization can beobtained from the SSI detection. If there is no AIT, the AIT physicalchannel (PACH) is monitored and detected. If there is an available AIT,the access configuration is read, for use with the following randomaccess, according to the selected SSI.

3.2.2.2.7 Managing SSI Reuse and Uniqueness

Other considerations include ensuring uniqueness of the SSI, e.g., bymanaging reuse of SSIs in a network. A UE using the access informationconfiguration of one SSI in one area, could access the same SSI in adifferent area where the SSI may have a different meaning e.g., point toa different access information configuration. Another consideration ishow to manage PLMN borders, where a UE may read a SSI of another PLMNand try to access using wrong access information.

3.2.2.2.8 Coverage Evaluations

Initial coverage results indicate that broadcast of system informationis costly at 15 GHz carrier frequency. FIG. 82 shows the required dutycycle for distributing AIT/SSI in a dense urban deployment, whereAIT/SSI is using 1.4 MHz of the system bandwidth (100 MHz). In thefigure, AIT is transmitted once per second; SSI a times. Thecorresponding LTE MIB performance requirements are used to determine thedesirable AIT/SSI duty cycle; AIT and SSI should work at the cell edge,which corresponds to 5^(th) percentile SNR of −16 dB and 5^(th)percentile SINR of −20 dB for dense urban deployments. For energyefficiency and capacity reasons the duty cycle of AIT and SSI should beas low as possible. In the energy efficiency evaluations, a duty cycleof a 1-2% has been assumed. The results in FIG. 82 show coverage can bemaintained with a duty cycle of a few percent for AIT/SSI transmission.However, to make this possible it is desirable to reduce the load onboth AIT and SSI and to reduce the periodicities of the same.

The results highlight the importance of minimizing the information to bebroadcasted in NX. The AIT/SSI solution allows separating thetransmission point of AIT and SSI, so that only SSI needs to betransmitted in the high frequency carrier, while AIT could bedistributed on a lower frequency carrier, via LTE or there could be aset of default SSIs defined in the standard for the initial access.

3.2.2.3 Alternatives

As an alternative to the index based (AIT+SSI) distribution of accessinformation, other distribution methods of system information can alsobe considered. The main benefits of the AIT+SSI based broadcast ofaccess information are that it can be very resource efficient, it canminimize the amount of broadcasted information in high frequencycarriers, it provides a framework for separating system functionalityand signals for system access and tracking and it can provide very goodnetwork energy efficiency.

Alternative solutions might be used, however. In one option, the systeminformation could still be encoded using the MIB/SIB based structure ofLTE. Note that this still allows for sending the SIBs that are notneeded for initial access using a dedicated high gain beam in highfrequency where beam forming is desirable for coverage. Network energyefficiency could be addressed by only distributing the accessinformation upon request from UE in areas with low traffic demands forenergy savings purposes. The solution could also be used jointly withthe index based approach. For this, the access node needs to send apre-defined synchronization sequence, so the UE can send a random accesspreamble. Beamforming and beam sweeping can be used to improve the linkbudget for the MIB/SIB transmission to the UE.

3.2.3 UE Camping

In LTE, the UE camps in a “cell”. Prior to camping, the UE performs acell selection which is based on measurements. Camping means that the UEtunes to the cell control channels and all the services are providedfrom a concrete cell and the UE monitors the control channels of aspecific cell.

In NX, different nodes may transmit different information. Some nodesmay transmit the SSI/AIT table, while others may not transmit SSI and/orAIT, for instance. Similarly, some nodes could transmit the trackinginformation while others may transmit paging messages. The notion ofcell becomes blurry in this context and, therefore, the concept of cellcamping is no longer suitable in NX.

The relevant signals the UE may monitor while in dormant state are oneor more of:

-   -   SSI    -   Tracking RAN Area Signal—TRAS (see section 2.2.4.1.1)    -   Paging Indication Channel/Paging Message Channel (see section        2.2.4.2.1) NX camping is, therefore, related to the reception of        a set of signals. The UE should camp on the “best” SSI, TRAS,        and PICH/PMCH. NX camping (re-)selection rules for these signals        are used, just as cell (re-)selection rules exist in LTE.        However, since the degree of flexibility is higher, these rules        may also be slightly more complicated.

3.2.4 DRX, Tracking and Paging

UE Tracking is used to assist the paging functionality. When the networkneeds to locate the UE, the network may limit the transmission of thepaging messages within the tracking areas which the network configuredfor the UE. There are at least three major reasons why thetracking/paging functionality was re-designed for NX:

-   -   1. NX design aims to be modular to avoid dependencies which        could limit future enhancements, and it should be future        compatible.    -   2. In Dormant state, it is assumed that a S1 connection is        established. This means that the paging responsibility is partly        moved from the CN to the NX-eNB.    -   3. System Access is based on a node transmitting a System        Signature Index (SSI) which points to an entry in the Access        Information Table (AIT). The AIT is a collection of the        different system information configurations related to the        network access which the network could have. This means that any        node may use any SSI depending on the network access        configuration which is to be used by the UE. In other words, the        SSI does not carry location information.

FIG. 83 illustrates possible SSI/AIT deployments that could both use thesame Tracking Areas configuration, e.g., the Tracking Areasconfiguration depicted in FIG. 84.

3.2.4.1 Tracking

Location information is desirable to assist the network to locate theUE. Solutions to provide location information using the SSI/AIT arepossible; however, at the cost of introducing certain constraints.Another solution is to use the SSI block. The SSI block could carry thecontent or part of the content described in the TRASI (see below). TheSSI block is independent of the SSI. Therefore, it could qualify as anoption to provide location information. Yet, another solution whichprovides a higher degree of flexibility is to introduce a new signal tocarry such information. This signal is in this context called TrackingRAN Area Signal, TRAS. The area in which this signal is transmitted iscalled Tracking RAN Area, TRA. A TRA may contain one or more RAN nodesas depicted in FIG. 84. The TRAS may be transmitted by all or a limitedset of nodes within the TRA. This also means that this signal and itsconfiguration should preferably be common for all the nodes transmittingthe TRAS within the given TRA, e.g., in terms of (at least) roughlysynchronized transmissions, to facilitate the procedures for the UE andaid it to reduce its energy consumption.

3.2.4.1.1 Tracking RAN Area Signal—TRAS

The Tracking RAN Area Signal (TRAS) comprises two components, a TrackingRAN Area Signal Synchronization (TRASS) and a Tracking RAN Area SignalIndex (TRASI).

3.2.4.1.2 Tracking RAN Area Signal Synchronization (TRASS)

In the Dormant State, prior to each instance of reading the TRA info,the UEs are typically in a low-power DRX state and exhibit aconsiderable timing and frequency uncertainty. The TRA signal shouldtherefore also be associated with a sync field that allows the UE toobtain timing and frequency synchronization for subsequent payloadreception. To avoid duplicating synchronization support overhead in yetanother signal, TRASI reception can use SSI for the purposes ofsynchronization in deployments where SSI and TRAS are transmitted fromsame nodes and are configured with a suitable period. In otherdeployments where the SSI is not available for sync prior to readingTRASI, a separate sync signal (TRASS) is introduced for that purpose.

The SSI design has been optimized to provide UE synchronization. Sincethe synch requirements for TRA detection, not least the link qualityoperating point for the UE and the required ability to read the DLpayload information, are similar, we reuse the SS physical channeldesign and reserve one, or a small number, of the PSS+SSS sequencecombinations to be used as the TRA sync signal. The SS detectionprocedure at the UE may be reused for TRA synchronization. Since TRASSconstitutes a single predetermined sequence, or a small number of them,the UE search complexity is reduced.

Information about whether TRASS is configured by the network may besignaled to the UE, or the UE may detect it blindly.

3.2.4.1.3 Tracking RAN Area Signal Index (TRASI)

The tracking area index is broadcasted. At least two components havebeen identified to be included in the TRASI payload:

-   -   1. Tracking RAN Area code. In LTE, a TA code has 16 bits. The        same space range may be used for NX.    -   2. Timing information (see section 2.2.4.3). As an example, a        System Frame Number (SFN) length of 16 bits may b used, which        would allow a 10 minutes DRX given a radio frame length of 10        ms.

The payload is thus estimated as 20-40 bits. Since this number of bitsis impractical to encode into individual signature sequences, the TRAinformation is transmitted as coded information payload (TRASI) withassociated reference symbols (TRASS) to be used as phase reference.

The TRASI payload is transmitted using the DL physical channelstructure:

-   -   Alternative 1 [preferred]: Use PDCCH (persistent scheduling).        The UE is configured with a set of 1 or more PDCCH resources to        monitor    -   Alternative 2: Use PDCH (persistent scheduling). The UE is        configured with a set of 1 or more PDCH resources to monitor    -   Alternative 3: Use PDCCH+PDCH (standard shared channel access).        The UE is configured with a set of 1 or more PCCH resources to        monitor, which in turn contain a pointer to PDCH with the TRA        info

The choice between PDCCH and PDCH should be based on whether reservingresources in one or the other channel imposes fewer schedulinglimitations for other signals. (For nomenclature purposes, the usedPDCCH/PDCH resources may be renamed as TRASI physical or logicalchannel.

TRASI encoding includes a CRC to reliably detect the correct decoding atthe UE.

3.2.4.1.4 UE Procedures

The UE uses its standard SSI search/sync procedure to obtain sync forTRASI reception. The following sequence may be used to minimize the UEenergy consumption:

-   -   1. First look for TRASS    -   2. If TRASS not found, look for most recent SSI    -   3. If same SSI not found, continue to full SSI search

In some UE implementations, the RF wake up time is the dominant energyconsumption factor, in which case full search may always be performed.

If no TRASS is present but several SSIs are audible, the UE attemptsTRASI reception at all found SSI and/or TRASS timings, one of whichsucceeds. All SSIs are detected and corresponding TRASI detection isattempted during the same awake period, so no RF overhead is introduced.

If “loose” sync with a known tolerance within a TRA is provided, a UEsearches for TRAS-related time sync in the relevant vicinity of thecurrent timing, plus the worst-case timing drift during the DRX. The UERX waking time is “proportional” to the timing tolerance.

3.2.4.1.5 Low SNR Operation

For TRASS, a low-SNR situation should be addressed similarly to SSI (seesection 2.3.4), since the signaling requisites for successfullyobtaining sync are the same.

For TRASI, one or both of two approaches are practical to cover suchlow-SNR scenarios:

-   -   1. Lower the rate of the TRASI signal to allow energy collection        over an extended time (e.g., repetition).    -   2. Apply beam sweep, repeating the TRASI information in a set of        relevant directions, where beam gain is applied in each        direction. (In this case, it is preferable to transmit TRASI on        PDCH which has been designed with beam sweeping support.)

Whether repetition is applied in the form of “omni-directional” low-ratetransmission or spatial repetition of higher-rate transmissions duringbeam sweeping, the worst-case reception time is the same. However, usinga beam sweep cuts the mean reception time in half.

3.2.4.1.6 TRA Configuration

TRA configuration should be identical within the TRA. This means thatall the nodes which transmit the TRAS should use the same configuration.The reason behind this is due to the DRX configuration. A UE in dormantmode wakes up for a certain period of time. In that period of time, theUE is expected to monitor and perform measurements as configured by thenetwork (or as mandated by the standard).

TRA configuration is conveyed via dedicated signaling. AIT is not themost suitable option to convey this information. The TRA configurationcould be transmitted to the UE, for example, when the network commandsthe UE to move from Active Mode to Dormant Mode or when the networktransmits a TRA Update Response to the UE. TRA Update Response—couldalso carry paging information (see FIG. 85). This could be especiallyuseful to minimize paging delays in situations when the network istrying to locate a UE in TRA which the UE has already exited. To be ableto support this type of functionality, the UE may need to add in the TRAUpdate some type of ID or other information to assist the new TRA ornode to identify previous TRAs or nodes which could contain the UEcontext, paging messages or user data. In FIG. 85, which illustrates aTRA update procedure, a UE moves from a TRA_A to a TRA_B which is notconfigured in its TRA list. When the UE has exited the TRA_A, but notregistered yet in TRA_B, the network starts sending paging indicationsover a certain node or set of nodes in TRA_A. The UE does not respondsince it has exited the TRA_A and may not monitor the TRAS_A any longer.When the UE performs a TRA Update, the network provides the new TRA listand configuration, and may further include any paging indications whichthe UE could have been missed.

3.2.4.1.7 Timing Synchronization Between TRA

The less synchronized the network is, the higher the UE battery impactis. Keeping a tight synchronization across TRAs is therefore importantbut also challenging, especially in deployments with poor backhaul.

A few options are listed below.

-   -   All TRAs are loosely synchronized.    -   No synchronization across TRASs.    -   Sliding synchronization across neighbor nodes.    -   Loosely synchronized within the TRA & not synchronization among        TRASs.

3.2.4.2 Paging

Paging functionality has one or both of two roles:

-   -   To request one or more UEs to access the network    -   To send notifications/messages to one or more UEs

AIT may not always be a suitable solution to deliver broadcast/warningmessages. There are a few reasons why:

-   -   One single node distributes the AIT in a large area. An update        on the AIT would mean that all the UEs within the AIT coverage        would acquire the AIT to collect the message. However, it would        be more challenging, for example, to distribute this        notification within a smaller area.    -   The NX concept allows long periods for AIT distribution. When        AIT is seldom distributed, the delay requirements for warning        messages may not be fulfilled.    -   AIT is expected to only carry the minimum possible information,        and current thinking is that the AIT size (at the air interface)        is, at most, a couple of hundreds of bits. This assumption is        not compatible with the fact that broadcast and warning systems        may require to transmit messages of several hundreds of bits.

The paging solution reuses the NX physical channel PCCH/PDCH butintroduces the following logical channels:

-   -   Paging Indication CHannel (PICH)    -   Paging Message CHannel (PMCH)

3.2.4.2.1 Paging Signals: PICH and PMCH

The general intention for paging signaling design is to enable receptionwith minimal UE energy consumption, preferably reading a single signal,while being resource-efficient for the network. In LTE, the UE firstneeds to read PDCCH information with a pointer to PDSCH resourcescontaining the paged UE list.

No new physical channels should be introduced for distributing paginginformation; the PDCCH and PDCH should be used for that purpose. PDCCHis expected to support message sizes up to 40-50 bits, which can providea resource allocation pointer to a PDCH, while PDCH can carry largemessages.

Due to the need to support a wide range of network configurations andlink conditions, a number of paging configurations are introduced,comprising two fields, PICH and PMCH, that assume different functionsfor the different configurations:

-   -   PICH: In a typical expected configuration, PICH is mapped onto        PDCCH. The paging indication may contain, depending on the        scenario/deployment and the amount of data to transmit, one or        more of the following: a paging flag, warning/alert flag, ID        list, and resource allocation.    -   PMCH: The PMCH is mapped onto PDCH. PMCH may optionally be        transmitted after the PICH. When the PMCH message is sent, it        may contain one or more of the following contents: ID list, and        warning/alert message.

3.2.4.2.2 Synchronization

PICH/PMCH synchronization may be achieved by different means dependingon the deployment scenario:

-   -   TRASS/SSI assisted: when paging signals are transmitted shortly        after the TRASS or SSI from the same node.    -   Self-contained paging: A separate sync signal (like TRASS)        preceding the paging should be introduced if nodes transmitting        paging do not transmit TRAS or SSI, or the period of those        signals is different than the paging period.

3.2.4.2.3 UE Procedures

The UE obtains sync using SSI or TRASS (-like) signal shortly beforereading paging. The UE is configured to monitor PICH according to theformat used by the network. Depending on the contents of PICH, the UEmay perform required actions and/or read PMCH. Reading PDCCH and PDCH isperformed in a standard manner, using the DMRS of the relevant RBs as aphase reference.

Based on the received paging channel contents, the UE may then accessthe network, read system information, perform other actions according tothe emergency messages, or do nothing. System access and system infoacquisition follow the usual SSI-based procedures.

3.2.4.2.4 Low SNR Operation

The options for handling TRASI in similar conditions apply here as well.Low-rate PICH transmission may mean sending a single-bit pagingindicator on PDCCH. PDCH may be the preferred medium if beamformingneeds to be applied to the PICH.

3.2.4.2.5 Paging Configuration

Paging configuration, like in LTE, also configures the UE DRX cycles.Paging configuration for UEs in Dormant state is provided to the UE theUE via dedicated messages e.g., in the TRA Update Response or other RRCmessages.

The paging configuration should be valid within a certain area(s) e.g.,a TRA. This information is also to be conveyed to the UE in the pagingconfiguration.

3.2.4.3 DRX and Paging in NX

One of the underlying and important assumptions is that NX and LTE aretightly integrated. Therefore, the scheme to configure DRX and Pagingcycles in NX is very similar as the one in LTE. In other words, pagingcycles and DRX cycles in NX are bound together and depend on the SFN.

The solutions proposed for tracking and paging allow all signals to betransmitted by any node independently from each other. In other words, anode transmitting one of them does not impose the transmission ofanother of the signals by the same node. This type of design imposescertain challenges and requirements:

-   -   The UE has to receive all the necessary signals during the DRX        “listening period”,    -   DRX cycle and paging cycle should apply within a certain region,        e.g., a TRA        -   Paging configuration should apply within that region        -   TRAS configuration should apply within that region        -   All nodes within that region have synchronized SFNs.

If SSI/TRAS/Paging signals are transmitted from different nodes or bycombinations of nodes, the network should ensure that all these nodesare coordinated and know the UE configuration.

For long DRX cycles, clock drifts are significant, and could be largerthan the period of the downlink signals. This introduces a possibleerror in the SFN calculation. If there is no SFN correction, the UE maymiss paging indications. This means that the SFN (or other timinginformation) should be included in the downlink signals, so when the UEwakes up, it can correct its drift and calculate the correct pagingframe.

Since the SFN information is used to calculate the paging/DRX cycles, itcould be reasonable to conclude that the SFN is to be introduced in atleast one of the signals which support paging/DRX. The SFN cannot beincluded in the paging signal since paging is not always sent by thenetwork. Therefore, the other potential signal to carry this informationis the TRAS. Depending on the deployment, e.g., the SSI and TRAS andpaging from the same node, the SFN could be contained in either the TRASor the SSI Block. See Section 2.2.2.2.4. Moving paging/DRX functionalityin dormant state to RAN has certain implications for the network. Forexample, RAN may need to buffer user plane data which could beconsiderable for long DRX cycles. In cases of long DRX in Dormant state,there may be also some impacts in the design of the core networkprotocols CP/NAS, and might be required the RAN to provide to CN nodesinformation about UE reachability (ref. High Latency Communicationprocedures in 23.682).

3.2.5 Connection Establishment

The procedure for connection establishment may vary depending on the UEstate and the deployment, both in terms of node transmit power andcarrier frequencies deployed. In this section, initial connectionestablishment is described for a UE in DETACHED state.

3.2.5.1 PLMN Selection

From a higher layer perspective, before the UE powers on, the UE is inDETACHED state; see state transition diagram in FIG. 3. When the UEpowers on it could either have LTE or NX carriers as highest priority toperform PLMN selection, according to what is configured in its USIM.

In the case of LTE, the PLMN selection is a well-known procedure wherethe PLMN associated to a carrier frequency is broadcasted in SIB1. Inorder to do PLMN selection the UE needs to perform L1 synchronizationusing PSS/SSS, then PCI detection to decode CRSs and perform channelestimation and decode System Information, more specifically the MIB andthen SIB1 broadcasted each 80 ms. This needs to be done for each carrierfrequency until the UE finds an appropriate PLMN that it is allowed toselect.

In the case of NX, different solutions are possible. These have takeninto account the different ways to distribute system information in NX;see 3.2.2.

Assuming an AIT/SSI based solution for system information acquisition,for each scanned frequency carrier the UE detects the AIT that containsthe PLMN. In order to allow the UE to quickly start scanning anothercarrier (if the previous one is not associated to an allowed PLMN) thePLMN can be encoded at the beginning of the AIT. A potentialdisadvantage is that to keep the same delay performance as LTE's PLMNselection, the AIT would need to be transmitted each 80 ms (e.g.,instead of a periodicity on the order of one or more seconds).Alternatively, the transmission of AIT can be aligned between differentPLMNs to minimize the PLMN selection time. To note here is that theinitial attach will be a rare event in NX, as the target is to keep UEsin dormant state; thus the delay performance of the attach procedurebecomes of less importance. Also, the design includes the possibilityfor UEs to store the AIT and use the SSI to check validity of stored AITwhen accessing the system, so that reading the AIT is not always neededwhen accessing from idle. In areas where PLMN search is more likely tooccur, e.g., at airports, the AIT period can be shorter.

An alternative is possible where for each scanned frequency carrier theUE detects PLMN-related information, preferably limited in number ofbits, transmitted more frequently than the remaining system information.When system information is distributed according to the AIT/SSIapproach, this limited information could be an SSI and the remaininginformation can be the AIT so the UE can check whether a given carrierfrequency belongs or not to its allowed PLMNs (stored in the USIM). Thisinformation can be used both to speed up the initial PLMN/RAT/Frequencysearch, as well as to avoid problems with re-use of system signatures(SSI) or other synch signals between operators (that can be reused).This PLMN-related information is preferably a compressed version of thePLMN list (which includes the Home PLMN). The compression can be madevery space efficient since false positives could be allowed (but notfalse negatives). Alternatively, the information can be the PLMN list,e.g., when space is not an issue or when only one or a few PLMNs arebroadcasted. This alternative solution in systems where plain systeminformation is distributed per-node like in LTE. In that case, the fewbits encoding the PLMN-indication can be transmitted more often, whichcould optionally be in areas where PLMN search are more likely to occursuch as areas close to airports.

3.2.5.2 Single Attach for LTE and NX

Once the UE has selected an allowed PLMN, the UE initiates an attachprocedure to access and register to the CN. Regardless of the accessedRAT, the attach is associated to both NX and LTE. In this process, acommon S1* is established, which is kept during the lifetime of the RRCconnection. The single attach allows a fast sub-sequent establishment ofdual connectivity between LTE and NX, when required.

Because of the tight integration with LTE, the RRC connectionestablishment procedure resembles that of LTE, except for theinformation carried in the messages. The procedure for the initialattach over the NX interface is shown in FIG. 86. On the other hand,some of the procedures (mainly from the perspective of lower-layerprocedures) are access-specific, such as coverage detection, PLMNsearch, system information acquisition, synchronization and randomaccess.

Access Information Acquisition

The UE starts by acquiring the needed access information to access theNX system, according to section 3.2.2. The SSI can be broadcasted ortransmitted in a wide beam (see section 3.4.4.2), or beamforming may beused in some specific scenarios.

The SSI implicitly provides the UE with information on how todemodulate, decode and descramble the AIT. One example alternative isthat the SSIs are grouped into sets of N (e.g., N=16), which all pointout the same AIT. In the AIT the UE finds configurations required totransmit the physical random access preamble and how to receive therandom access response (steps 1 and 2 in FIG. 86, respectively).

1. Physical Random Access Preamble Transmission

FIG. 87 illustrates random access preamble transmission. The physicalrandom access preamble is transmitted based on a time reference from aSSI or specific PRACH indication signal. If beam forming is used and ifthe eNB only supports analog or Hybrid BF, the preamble transmission maybe repeated to allow for beam sweeping. If beam sweeping is also usedfor SSI transmission, the timing offset from the SSI to preamble canalso be utilized. This downlink reference signal is also used as a powercontrol reference and layer selection for the transmission. A preambleis selected based on the SSI and the Access Information Table entry. Thepreamble format is described in 2.3.4.2. As shown in FIG. 87, thetransmitted preamble may be received by multiple network nodes.

2. Random Access Response Transmission

FIG. 88 illustrates random access response transmission. The randomaccess preamble transmission is followed by a search window in time andfrequency where one or multiple Random Access Response (RAR) messagescan be received. The RAR transmission can be beam formed based on PRACHchannel estimation assuming UL/DL reciprocity. The RAR isself-contained, in that it carries its own sync and demodulation pilots,and the UE blindly searches for a set of such pilots associated with theSSI and the selected preamble index. If more than one network nodereceived the random access preamble, network coordination can be appliedto limit the number of RAR transmissions—see ID2 in the left part ofFIG. 88. If more than one RAR is received—see the right part of FIG.88—the UE performs a selection step to find the RAR to comply with. TheRAR also contains a timing advance command to adjust the uplink timingand a scheduling grant for next uplink message. The RAR message includesa downlink PDCCH/PDCH configuration and an uplink PDCH configuration;sub-sequent messages use configurations provided in the RAR. Theseconfigurations can be derived from a single index e.g., a “radio linkconfiguration index” (that is similar to the PCI in LTE).

3. RRC Connection Request

Upon receiving the random access response, the UE transmits the RRCConnection Request message, including a CN level UE identity (e.g.,S-TMSI) requesting the setup of the RRC connection.

4. RRC Connection Setup

The network responds with RRC connection setup to establish SRB1. Thisstep is also the contention resolution step, which is used todifferentiate between two UEs having transmitted the same preamble andalso selected the same RAR. This is done by resending the CN level UEidentity included in the RRC Connection Request message and the RRCconnection ID; see section 2.1.3.1.1.

5. RRC Connection Complete

The UE completes the procedure by sending the RRC Connection Completemessage.

6. Common Security Setup

Security signaling is discussed in section 2.1.5.2.

7. Common UE Capability UE capability signaling is discussed in section2.1.5.3.

8. RRC Connection Reconfiguration

An RRC connection reconfiguration procedure is performed to configureSRB2 and the default RB. User plane transmission is possible after thisprocedure. Note that all CN signaling was not detailed in this briefdescription. In general, due to the tight integration, we expect the CNsignaling to be backward compatible with LTE CN signaling.

3.2.5.3 Accessing NX Carrier

This section discusses NX carrier access, which is a component ofseveral connection establishment procedures:

-   -   Case A: UE performs the single attach over NX, e.g.,        DETACHED→RRC_CONNECTED ACTIVE transition, and needs to access an        NX carrier that could be in low or high frequency layer.    -   Case B: UE performs the RRC CONNECTED DORMANT→RRC CONNECTED        ACTIVE transition and establishes a link with an NX carrier.    -   Case C: UE in RRC_CONNECTED ACTIVE having a primary carrier        establishes a secondary carrier (that can be in higher        frequencies). This could be seen as similar to the setup of a        secondary carrier as in LTE CA.

The common aspect of the abovementioned scenarios is that the UE needsto access an NX carrier which could be in a wide range of frequencies. Afirst step before the UE can access the NX carrier is to detect thecoverage, typically done via the monitoring of some transmitted signals.These can be either i) common, ii) dedicated or iii) defined per groupby the network. In the NX case these are either SSIs or MRSs.

These signals may also differ in the way they are transmitted by thenetwork. In higher frequency, for example, these signals can betransmitted using narrow beamforming (which would require a beamsweeping procedure for coverage detection, see section 3.4.4), orbroadcasted (where some repetition could be desirable for worst caseusers). At lower frequencies, these signals could be broadcasted andless repetition may be used for worst case users, since propagation isless challenging. It can be beneficial to have a harmonized solution forthe different carriers where the UE procedure for coverage detection isexactly the same, regardless the way the network provides the coverage.

Despite the commonalities of cases A, B and C there may still be somecase specific issues, especially in deployments where the signals usedfor coverage detection need to be beam-formed (coverage only provided byan NX carrier in a high frequency in some specific ISD).

Case C is the least challenging since the UE already has an active RRCconnection and can be configured to search for specific NX signals,e.g., beam-formed MRSs. In that case, system information about how toaccess that beam (e.g., some sort of PRACH configuration towards thatbeam) can also be informed via dedicated signaling. In the case thesecondary NX carrier is deployed in another node, some network signaling(e.g., over X2*) may be used. The establishment of the secondary NXcarrier may occur with an RRC re-configuration, similarly as theestablishment of inter-frequency DC. In another alternative, the UE caninstead directly access the beam and rely on some context fetching.

Case B is challenging since the UE needs to establish a link with NXwithout the support of an active RRC connection. From a higher layerperspective, this is described in section 2.1.5.6 (RRC Re-Activationprocedure). From a lower layer perspective there could be different waysto access the NX link. If the UE is configured to camp on a lowfrequency NX carrier (or in a high frequency carrier where thedeployment allows the broadcast of SSIs) state transition occurs via SSIsynchronization and random access procedure, as described in section3.2.5.2.

If the UE is configured to camp on a high frequency carrier, where evenlow rate channels need to be beam-formed to reach proper coverage, thestate transition needs to rely on beam sweeping/finding; see section3.4.4. Therefore, two alternatives are possible: an SSI-based access(preferred choice) but with a specific configuration where differentSSIs are associated to different beams with different RACHconfigurations, or an MRS-based access where the UE is configured todirectly perform a random access towards a pre-configured set of MRSs(e.g., within a TRA). The SSI-based access is the preferred choice, butthe MRS-based alternative provides additional flexibility e.g., tightthe access to location and on demand activation.

Case A is the most challenging, where the UE may need to access an NXcarrier in the higher frequency without any prior knowledge about thedeployment.

3.3 Protocol and Resource Partitioning for Different Services

This section discusses methods for resource participation andoptimizations for different services. The section is separated intothree subsections, where 3.3.1 discusses higher layer aspects such asnetwork slicing and multi-service support, while 3.3.2 and 3.3.3 look atpossible resource partitioning solutions on MAC and physical layers,which can be used to support different network slices and services.

3.3.1 Network Slicing and Multi-Service Support

NX supports a wide range of services and associated service requirementsin a wide range of scenarios. A single NX system could, for instance, atthe same time support M-MTC, C-MTC, MBB and various media use cases.

One way to address these different use cases is through the use ofnetwork slicing. Network slicing is an End-2-End approach where the useror operator of a network slice (e.g., a MTC sensor network) sees thenetwork slice as a separate logical network having similar properties ofa dedicated network (e.g., separate management/optimization), but wherethe network slice is in fact realized using a shared infrastructure(processing, transport, radio) that is shared with other network slices.From a functional domain, the network slice can be realized withdedicated or shared functional components (such as eNB, EPC). Typically,a network slice may have its own CN (EPC) instance, but share thephysical transport network and the RAN. However, other solutions arepossible. In the event that a functional component is shared, it ispossible via parameterization to configure the expected slice specificbehavior for that shared component.

FIG. 89 illustrates examples of different services realized in differentlogical network slices, using common infrastructure resources andcomponents

Where different slices use different CN instances, it is possible toapply slice specific optimizations with regards to the functional scopeand the deployment of the different CN instances. This is illustrated inFIG. 90. In this example, for instance, use case X can have a differentinternal CN architecture and functions, which are also deployed muchcloser to the radio compared to the MBB slice. To enable support fordifferent CN instances, in the RAN there is a slice selection mechanismto steer different users to different CNs. (Note that this drives arequirement for new functionality in the S1* interface, compared to thecurrent S1 interface.) In addition to a mechanism for slice selection,the RAN also supports a mechanism to manage resources usage betweenslices. These mechanisms are controlled by operator policies.

It is preferred that all slices support the same CN/RAN interface (e.g.,S1*). FIG. 90 illustrates an example of network slicing using differentEPC instances optimized for different use case

In scenarios where the RAN supports multiple slices it is important thatthe shared resources, such as spectrum, are used efficiently between theslices, and that static or slowly changing allocations of resources todifferent slices are avoided. Only in exceptional cases should resourcesbe reserved to one slice, such that they cannot dynamically be used byother slices. Example of such cases can include when the users in oneslice require a special numerology or use a different MAC mode. Whendynamically shared resources are used, it is possible to define aminimum share of resources to a slice during times of congestion. Inorder to be able to apply these types of slice related policies, the RANneeds to be aware of a slice ID.

In addition to different shares of resources for different slices, theRAN can also provide different slices with different MAC and physicallayers. This is discussed in sections 3.3.2 and 3.3.3.

In addition to network slicing, NX also supports QoS differentiationwithin the same network slice.

3.3.2 Multiple MAC Modes and Radio Resource Partitioning 3.3.2.1Motivations and Scope

NX is designed to allow flexible sharing of the radio resources betweenservices with diverse requirements on, for example, delay andreliability. However, despite being supported by NX, in some practicaldeployments, for some critical use cases (e.g., intelligent transportsystem, public safety, factory automation, smart grid) it may not beacceptable to coexist on the same frequency or even carrier with anyother service. For this purpose, it may be desirable to operate certainservices on dedicated frequency (sub-) bands or even on a dedicatedcarrier. Separating the radio resource in this manner may also enablelower complexity implementation and testing in some situations. However,it should be stressed, the default assumption still is the dynamicsharing of resources between services and limiting services to sub-bandsor even separating them on different carriers is the exception and onlyapplicable in extreme cases.

The multiplexing of services, either to support the network slicing (see3.3.1) and/or multi-service support or for the support of different UEconfigurations, can take the advantage of the following approach toradio resource partitioning. This is in line with the stay in the boxprinciple for Layer 2 (see 2.2), and the basic idea is to divide theavailable radio resources into different partitions, each being used fora given MAC behavior.

As introduced in 2.2.1, a service-centric approach is desired to copewith all the possible aspects of scheduling a global network may face.

Numerous types of services can exist within the same network, andcombinations of these may have to be served at the same time. All theseservices (e.g., MBB, C-MTC, Voice . . . ) have different performancerequirements (e.g., latency, reliability, throughput . . . ), whichtranslate into various radio resources usage requirements (TTI, Resourceblock size, Prioritization . . . ). This is illustrated in FIG. 91,which illustrates a diversity of services with their typical resourceusage.

Creating predefined resource partitions for different services is, ingeneral, a sub-optimal solution. It can be used to simplify the resourceallocation in the scheduler if the overall complexity becomesunbearable. However, the use case described here is to support thecreation of partitions of resources when the service requirements imposeit. Such cases can include, for example:

-   -   When the physical resources have different properties, such as        different numerologies;    -   When the service has very strong availability requirements        (e.g., access delay so short that it needs a constant resource        grant), such as C-MTC;    -   When the scheduling/signaling is handled in multiple nodes (D2D,        distributed MAC, etc.)

When a service or UE is served by a dedicated resource partition, itsview of the resource can be simplified, as shown in FIG. 92. Note thatthe resource partition doesn't have to be done in time or frequencydomain.

This approach also ensures that next generation of mobile network isprepared, not only for a gradual introduction of new services, but alsofor a gradual deprecation of features, as more efficient solutions aredeveloped. This can be achieved by assigning the MAC responsible for thenew solution to a gradually increasing set of physical radio resourcesat the expense of the physical radio resources assigned for the MACresponsible for the old deprecated solution.

3.3.2.2 Multiple MAC Modes and Resource Partitions

For a given UE or service, a MAC behavior can be configured followingspecific requirements. Different MAC behaviors can be related to:

-   -   different MAC schemes, e.g., contention-based versus scheduled        based,    -   different procedures for a scheme, e.g., RTS/CTS versus        Listen-before-talk,    -   different parameters used, e.g., timing, prioritization,        resource location . . .

By assigning a separate set of physical radio resources to a given MACbehavior, the MAC solution can be optimized only for requirements thatare relevant in that particular special case. The physical radioresources are “allocated” or “delegated” to each particular MAC. From anetwork perspective, the scheduling entity has to implement and processall the active MAC behaviors, but for each of these, behaviors can beprocessed independently.

Although having predefined partitions for resources is sub-optimal, thismay be useful in some scenarios since it enables a significantsimplification of the scheduling, as well as a diversity of possiblescheduling implementation. For instance, considering the case where ascheduled MAC and a contention-based MAC coexists, the contention-basedMAC scheduling is actually a distributed process, and not all the nodeshave direct access to the scheduled MAC information.

To limit the burden of predefined resource partitioning, the partitionbetween different MAC behaviors needs to be dynamically handled in thesystem. The resource partition and MAC mode selection can be done ondifferent level of scopes and updated with different frequencies. Forinstance, it can be done within a single cell or among a cluster ofcooperating cells; and with short or long term resource partitions (toadapt to specific local traffic requirements or to global trafficexpectations. For partitions made across cells, coordination between eNBis required. From the UE side, a communication/handshaking should bedone between the UE and AP (or UE to the serving node in case of relayor UE to UE . . . ) to agree on the service and related MAC behavior.

Following the stay in the box concept, each MAC partition needs beself-contained, with all the control mechanisms, pilots, and signalingthis implies—since different MAC behavior may require different type ofcontrol or information, it is easier that all are independent to eachother. Preferably, the MAC schemes are not allowed to transmit anythingon the other MAC's resource, so that each process enjoys cleanresources.

An example of MAC resource partitioning can look like FIG. 93, where theradio resources are partitioned in the time domain. The partitioning canbe done in any domain (frequency, time, space, code . . . ), notnecessarily in the time domain, although time may be easier to handlefor duplexing issues.

3.3.2.3 MAC Mode Selection

Which MAC mode or behavior is chosen for each node or service can dependon one or more of multiple factors:

-   -   The service or node requirements. As mentioned, the service        requirements of the user's traffic are an important criterion        for the design of the MAC behavior.    -   The supporting cell state. The load and link topology of the        serving cell (or associated with the serving node) can have an        impact on the performance of various MAC schemes. In the        scheduled vs. distributed MAC opposition, it is known that        distributed MAC is efficient and simple when the load is low or        when the hierarchy between the links is not straightforward        (presence of wireless backhauling, relay, D2D, etc.), while the        scheduled MAC is more efficient in cases of heavy load and when        uplink/downlink multiplexing doesn't need large cooperation. As        another example, if the node is located near several other nodes        or is subject to interferences (typically in the cell-edges),        modes that are robust or avoiding interference are preferred,        such as contention-based MAC or Scheduled MAC with coordination.    -   The network state (spatial coexistence). As another        complementary use case, using multiple MAC modes can allow the        coexistence between different parts of the networks. For        instance, considering an eNB close to two cells with distinct        MAC modes, it can choose to use a mixed MAC mode (partition of        multiple MAC), to accommodate both neighbors. This is a case of        spatial coexistence use. This spatial coexistence can apply        within the same network, but also for coexistence across        networks (typical of unlicensed bands). FIG. 94 illustrates        multiple MAC mode spatial coexistence.

3.3.2.4 Information Exchange and Signaling

The information exchanges can contain local information, localrequirements or local view of the system specific to a node or a groupof node in the cluster. A cluster coordinating point (CCP)/functionalitycan be established to facilitate the coordination of the radio resourcepartitioning and the MAC mode selection.

As described previously, the selection of the MAC mode or behaviordepends on the service or user, but may also depend on the serving cellor network state. This information has to be propagated among thecoordinated nodes.

In addition, how the resources are actually partitioned, in some cases,has to be known by all the concerned nodes in the system, and the nodesperforming resource partitioning should be aware of nodes and linkconditions to perform efficient decisions. This is particularly the casewhen the scheduling decisions are not made at a single place. Forinstance, if one MAC behavior is distributed (e.g., contention-based)all the nodes following this behavior have to be aware of when and wherethey are allowed to transmit/receive signals.

Two signaling methods are possible for communicating the resourcepartition to the UEs.

-   -   The first would rely on Layer 2 management, and let the eNB        scheduling messages include the radio resource partition        information. In this case, the resource partition between the        different MACs can be directly ordered from classical scheduling        messages, such as the dPDCH that can contain the scheduling of        the partitions. This leads to having a main Scheduled MAC, like        the classical cellular MAC scheme running as “default” and being        responsible to delegate parts of the radio resources to other        MAC schemes—or least being responsible of the delegation. These        dPDCH can indicate which resources used for a given MAC. The        advantage of L2 management is to have a per-TTI dynamicity of        the MAC allocation if needed, as well as a larger flexibility in        the message information provided in the dPDCH.    -   The second would rely on Layer 3 management and signaling, and        let system configuration typically provided in dedicated        messages includes the radio resource configuration. In this        case, system information concept is responsible to inform all        users of the structure. The advantage of this method is the        stability of the scheduling allocation, which can help all the        nodes and MAC processes to have a better forecast of the        resource availability. This also keeps all MAC totally        independent by preventing from having a “default” MAC        responsible to delegate resource to others. This however leads        to a slower flexibility and increase the number of possible        broadcast messages that require strong standardization.

3.3.3 Mixing of Different Numerologies 3.3.3.1 Introduction

Because of differences of latency, reliability, and throughputrequirements the 5G use cases require different symbol and framestructures (numerologies). Simultaneous support of 5G use cases andservices is a requirement and so NX is designed to supportsimultaneously multiple numerologies. As far as possible, resourcesshould be dynamically allocated between services to match demand.

3.3.3.2 Numerology and Transmission Format

Critical machine-type communication is expected to happen below 10 GHz.For wide area deployments at the lower end of this range, 16.875 kHz isthe default starting point; see also Section 2.3.2, where the differentnumerologies and their anticipated usage are detailed. Here the subframeduration is 250 μs, which allows for a sufficiently low latency for mostuse cases. Even shorter subframes can be realized with the 67.5 kHznumerology, which provides subframes of 62.5 μs (“67.5 kHz, normal CP”or “67.5 kHz, long CP”) or 125 μs (“67.5 kHz, long CP b”). One drawbackof the 67.5 kHz numerology over the 16.875 kHz numerology is theincreased overhead: It increases from 5.5% in “16.875 kHz, normal CP” to40.6% and 20.5% in “67.5 kHz, long CP” and “67.5 kHz, long CP b”,respectively. This assumes a deployment where a cyclic prefix in theorder of 3 μs is required where “67.5 kHz, normal CP” with 0.8 μs cyclicprefix cannot be used. If a cyclic prefix of less than 0.8 μs issufficient than “67.5 kHz, normal CP” can be used which has the sameoverhead as “16.875 kHz, normal CP”.

Often, a latency-critical machine-type communication (requiring 67.5 kHznumerology) requires only a fraction of the complete carrier. Theremaining part of the resources are used for less delay-sensitiveservices such as mobile broadband or other—lessdelay-sensitive—machine-type communication. It is therefore beneficialto use the 67.5 kHz numerology only for that part of the carrier thatserves extremely delay-critical services and “16.875 kHz, normal CP”numerology for the remaining part; see section 2.3.2.3. This enablesextremely short latency for the latency-critical machine typecommunication, but keeps the cyclic prefix overhead low for other—lessdelay-critical—services. Frequency-domain mixing of numerologies isimplemented with Filtered/Windowed OFDM; see section 2.3.1. Since thesubcarriers of the two numerologies are not orthogonal, a guard bandshould be inserted (˜10 subcarriers is desirable). As shown in FIG. 95,the partitioning appears static, however, as shown in FIG. 96 thepartitioning can change on a longer subframe basis (250 μs for mixing of16.875 kHz and 67.5 kHz). This is possible since both numerologies arealigned at the longer subframe boundaries.

In the example shown in FIG. 95, two OFDM numerologies are mixed on thesame carrier. In this example “16.875 kHz, normal CP” and “67.5 kHz,long CP b” are mixed. A guard band (grey) is inserted between thenumerologies. In the example shown in FIG. 96,the partitioning betweenthe two numerologies changes dynamically at longer subframe boundaries(250 μs). In this example “16.875 kHz, normal CP” and “67.5 kHz, long CPb” are mixed. A guard band (grey) is inserted between the numerologies.

The case where each subframe contains only one numerology, butnumerologies (may) switch at subframe boundaries is referred to astime-domain mixing of numerologies. Hardware limitations (e.g., linearpre-distortion) may restrict how often numerologies can be changed.

The above description is valid for the use case of mixing mobilebroadband and delay-critical machine-type communication in a wide aredeployment requiring a cyclic prefix in the order of 3 μs. For smallcell deployments with less delay spread where “67.5 kHz, normal CP”provides sufficiently long cyclic prefix (0.8 μs) the complete carriercan operate with “67.5 kHz, normal CP” eliminating the need forfrequency-domain mixing of numerologies.

In general, it is expected that frequency-domain mixing of numerologiesis only needed to address the most extreme requirements and singlenumerology or time-domain switching can address most use cases.

3.3.3.3 TDD Specifics

In a TDD system, resource availability for the two link directionsalternates in time. Support of very low latency in TDD requires frequentavailability of resources in the direction serving latency-criticaldata. Support of low latency in both link directions requires very shorttime durations per link direction and frequent switching between them;see FIG. 97, which shows that to support low latencies in TDD the linkdirection is switched every subframe. Every switch in a TDD systemrequires a guard period; hence increased switching frequency leads toincreased overhead. The fastest switching periodicity is achieved byalternating link direction every subframe. Per UL subframe, one OFDMsymbol duration is distributed as guard period among DL/UL and UL/DLswitches and the remaining OFDM symbols are used for UL traffic. Most ofthe numerologies have 4 OFDM symbols per subframe (except those withextended cyclic prefix, which have 3 or 7 OFDM symbols per subframe);the switching overhead thus becomes 12.5%, not only for the consideredlink but for all links served by the base station.

Furthermore, in non-isolated TDD deployments even adjacent channel TDDsystems need to adopt this very frequent switching ratio. Depending onthe reliability requirements, even TDD systems operating on further awayfrequency channels need to be synchronized. Services requiring extremelylow latencies are therefore preferable served via an FDD network.

The switching periodicity imposes also restrictions on the subframeduration. For example, if the switching is done every subframe of the“67.5 kHz, normal CP” numerology (62.5 μs) only numerologies withsubframe durations of equal to or less than 62.5 μs can be used.

3.4 Multi-Antenna Technologies

In section 3.4.1, an overview of the multi-antenna technologies in NX isprovided. In section 3.4.2, the central point of reciprocity isdiscussed. In section 3.4.3, three conceptual modes for acquiring CSI atthe eNB and designing beamforming for dedicated data transmission areelaborated. In section 3.4.4, three corresponding conceptual modes forUE transmit beamforming are described. In section 3.4.5, themulti-antenna perspectives of other procedures than data transmissionare given. In section 3.4.6, some multi-antenna hardware andarchitecture aspects are discussed.

3.4.1 Overview

Multi-antenna technologies have an instrumental role in the design ofmodern RATs due to their well-recognized benefits. Specifically, theyenable array gain, spatial multiplexing, and spatial diversity, whichlead to improved coverage, capacity, and robustness. The multi-antennafeatures have significantly contributed to the success of LTE andcontinue driving its evolution to Re113 and beyond. Multi-antennatechnologies have an even larger relevance in the design and performanceof NX due to a multitude of factors that are highlighted in theremainder of this section. These factors pose several design challenges,but also provide solution opportunities in the multi-antenna domain.

Driven by the 5G MBB requirement for Gbps peak rates, NX will be firstdeployed at new spectrum >3 GHz, mainly due to the availability oflarger bandwidth. However, extending the operation to >3 GHz also poseschallenges due to worse radio wave propagation conditions, e.g., thediffraction and propagation loss increase considerably. One way toovercome the link budget loss is to use UE-specific beamforming at theeNBs for both transmission and reception. While this is already includedin LTE, NX provides higher beamforming gains due to the large number ofantenna elements that arrays need to have to maintain the effectiveantenna area at a reasonable cost at high frequencies. The physical sizeof the antenna array though is expected to have similar size, or evensmaller at very high frequencies, since this is important for deploymentaspects such as ease of installation, wind load, and visual footprint.

The spatially focused transmission and reception, achieved byUE-specific beamforming from large arrays, is not only required to uselarger bandwidths that are only available at higher frequencies, butalso enables spatial multiplexing. Increasing the spectral efficiency,in particular by means of MU-MIMO, is an important design goal for NX tomeet the 5G MBB capacity requirements. There are at least two majorfactors that contribute to making this goal viable.

The first factor is the technology evolution towards large-scale activeantenna systems, also referred to as massive MIMO, in which several tensor even hundreds of antenna elements or small subarrays, can beindividually accessed, even directly from the baseband for digitalimplementations. This gives massive degrees of freedom to signalprocessing procedures which greatly enhance the interference reductioncapabilities. Moreover, the use of a very large number of antennaelements raises opportunities for reducing complexity and powerconsumption, and at least partially overcoming the HW impairments; thusenabling use of components with relaxed requirements. The second factorthat enables the goal of meeting the NX MBB capacity is that since mostof the new spectrum is expected to be unpaired, NX uses TDD. Highquality CSI is desirable to further improve the performance potential ofmassive MIMO signal processing capabilities. TDD facilitates theacquisition of explicit CSI, by making it possible to achieve thestrongest (so-called coherent) form of reciprocity, especially for largearrays for which feedback-based schemes may have significant signalingoverhead. Explicit CSI makes it possible to design flexible precodersthat exploit angular spread and suppress interference. In order to relyon reciprocity for CSI acquisition, special requirements need to beimposed to NX uplink signaling and HW design.

NX multi-antenna technologies are relevant, not only for eMBB, but alsofor C-MTC. Receive beamforming is well known to enhance robustness bymeans of spatial diversity, and transmit diversity can be used toimprove reliability of downlink transmissions. Exploiting reciprocitycould allow efficient and robust design, while feedback-based schemesare hampered by the stringent requirements that C-MTC puts on thefeedback reporting.

Also, NX multi-antenna technologies are not confined only to high-gainbeamforming and high-order spatial multiplexing. For procedures such asrandom access and broadcasting of control information or when CSI isless reliable, a wide (low-gain) beam pattern may be preferred, e.g.,over sequential beam scanning. By proper selection of precoder one cangenerate beams with variable-width. Furthermore, NX should not be tiedonly to fully-digital implementations; for several use cases, e.g.,indoor deployments operating at mmW frequencies, hybrid analog/digitalarchitectures offer attractive cost-performance trade-offs. Last but notleast, NX is expected to be able to capitalize on deployed sites,operate at existing FDD spectrum, and possibly reuse LTE HW platform. Inthese cases, NX multi-antenna technologies stem directly from thestate-of-the-art LTE ones, but are being adapted to NX design principlessuch as lean and self-contained transmissions, since NX does not have tothe backwards compatibility requirement.

It is important also to note that NX multi-antenna technologies do notonly refer to the eNB. Small wavelengths make viable even for handheldUEs to be equipped with one or more arrays with many active elements,possibly with distributed power amplifiers. Then, UL transmitbeamforming becomes a highly relevant feature, e.g., to improve uplinkcoverage of power-limited UEs. Moreover, in several 5G use cases (e.g.,self-backhauling, D2D, V2X, fixed wireless) the classicaldownlink/uplink notion of cellular access is not as relevant, as the twosides of the link may have similar multi-antenna capabilities.

In conclusion, due to the diverse requirements, the NX multi-antennatechnologies are a tool set of solutions with several flavors, ratherthan “one solution fits all”. The common denominator is though that itis possible, when relevant, to use antenna arrays to beamform allchannels that benefit from doing so in a given deployment.

3.4.2 Reciprocity

A broad definition of reciprocity is when an estimate of the UL channelcan be used when designing the DL transmission. We can think ofdifferent “levels” of reciprocity which are summarized as follows:

-   -   “Coherent” reciprocity: RX and TX channels are the same as seen        from baseband (within coherence time/bandwidth);    -   “Stationary” reciprocity: Channel covariance matrix is the same        for RX and TX;    -   “Directional” reciprocity: Angles of arrivals/departures        (AoAs/AoDs) are reciprocal for RX and TX.

Coherent reciprocity is the strongest form of reciprocity and it is onlypossible to achieve in TDD. It is very interesting to NX as it providesanother means, rather than closed-loop feedback, to obtain explicit CSI;thus enabling the full potential of the digital massive MIMO data modedescribed in section 3.4.3.3. The signaling overhead of the twotechniques scales in different ways; namely, with the number of eNBantennas for feedback and with the sum of number of UE antennas forreciprocity. The techniques are complementary and one can be preferredover the other depending on the use case.

Coherent reciprocity is not only the strongest but also the mostchallenging form of reciprocity to achieve. The propagation channel,including the antennas, is indeed reciprocal. However, hardware istypically not reciprocal. Reciprocity involves the complete RX and TXchains. There will be impairments that affect performance in thatreciprocity will not be ideal, putting requirements on calibration atthe eNB and UE sides. Some of the issues that could come into play hereare:

-   Power switching in the UE (normally the phase jumps depending on the    power);-   RX AGC switching;-   Phase ripple in filters (when UL and TX have different filters).    One or more of these should be addressed.

Directional reciprocity can be assumed quite safely in TDD, also outsidethe coherence time and bandwidth, and in FDD. This is because AoDs andAoAs appear to be reasonably similar even when changing the carrierfrequency over a large range, e.g., 6-100 GHz. This is a fact that could(and probably should) be exploited to a much larger degree thanconsidered so far in the concept work. One example is when alow-frequency (LTE) system is used in parallel with a high frequency NXsystem. DoAs or beam identities could be shared between the systems.Another example relates to CSI acquisition; AoD/AoA can be estimatedfrom RSs in one (narrowband) part of the bandwidth and used over thefull bandwidth. This could ease the overhead significantly. Accuracy ofresulting CSI depends on the circumstances, e.g., frequency differencebetween UL & DL and angular spread, as it is not realistic to assumethat we can estimate all AoAs accurately.

Stationary reciprocity can also be considered if the gap between the DLand UL bands is not too large and/or there is low angle spreading. Thisgives, additionally to the directional reciprocity, information on theamplitudes of the AoAs and AoDs.

Reciprocity-Based Reliability and Robustness for C-MTC

It is known that for a system based on fixed antennas, high diversity isdesirable to achieve very low error rates; for C-MTC see sections2.3.3.2, 2.3.4.1, 2.3.5.1, and 3.1.7. The diversity track is judged tobe quite safe, but resource inefficient. The problem for C-MTC, or lowerror probabilities in general, is that every delay and step in a CSIacquisition process gives potential error cases. If we considertraditional CSI feedback information these messages are quite comparablein the number of bits as a C-MTC message and also need robust encoding.An alternative is to use reciprocity that effectively “short-cuts” onestep in the CSI acquisition process. Reciprocity-based schemes can thusbe used to find and utilize the channel characteristics more selectivelyand maybe hence lower the cost for C-MTC dramatically.

Another question is how hardware related issues like dynamic range andhardware reliability impact the design and how they are handled. Again,there is a large potential in reciprocity-based schemes as they can (ata hardware overhead cost) be used to get channel knowledge to manybase-stations without any additional radio resource cost.

3.4.3 Dedicated Data Transmission

In this section, three modes for dedicated data transmission aredescribed, with particular focus on the CSI acquisition. Together, thesethree complementary modes cover the foreseen multi-antenna solutions fordeployment scenarios and antenna architectures. Each of the schemes hasits advantages and drawbacks. The element-based feedback, beam-basedfeedback, and coherent reciprocity-based massive MIMO are described insections 3.4.3.1, 3.4.3.2, 3.4.3.3, respectively.

3.4.3.1 Element-Based Feedback

Assume that the hardware architecture is similar to that of atraditional LTE platform. In this case, the assumption is that the bestLTE feedback MIMO solutions are carried over without the legacy overheadof LTE, and used with an element-based feedback scheme. Here, an antennaelement can mean a single radiating element, or a sub-array of radiatingelements. The antenna patterns are fixed or very slowly varying and allof the limited number of TX/RX chains are possible to exploit inbaseband. See FIG. 98, option 1, for an example with 8 TX chains.Herein, it is assumed that the number of TX chains is limited to amaximum of 8. Foreseen examples where an element-based feedback schemewould be more appropriate are:

-   -   Nodes operating in FDD with a small number (˜10) of antenna        elements;    -   Nodes operating in TDD with a small number of antenna elements,        where coherency cannot be maintained; in practice, this means        that hardware calibration is not used;    -   Nodes with a small number of antenna elements, where UL/DL        decoupling is applied, since reciprocity cannot be used then;    -   Nodes where we try to maximize similarity with LTE, perhaps to        the extent to reuse the LTE hardware;    -   Scenarios when the node or UE cannot sound all RX/TX chains due        to limited TX capabilities.

In summary, an element-based feedback scheme is used when coherentreciprocity cannot be used, or when the number of antenna elements issmall. For larger number of antenna elements beams are formed usingother feedback mechanisms, e.g., beam discovery or explicit feedbackmechanisms, as described more in section 3.4.3.2.

It may be surprising to aim to support element-based feedback for onlysome 10 antenna elements, as LTE already supports 16, and soon evenmore. The reason for not advocating element-based feedback for largernumber of antennas is the lack of flexibility that arises from definingthe codebook in the standard: the defined codebook is only defined for acertain antenna size, and is only optimum for a certain antenna layout.Here, the beam-based feedback scheme offers more flexibility, bothregarding antenna size and antenna layout.

The main differentiating aspect in handling precoder feedback in NXcompared to LTE is in scenarios with more UE antennas and multiplespatially separated eNB transmission points (possibly non-coherent),each with a number of antenna elements. In such case, multipleindependent precoders could be signaled due to the fact that thechannels in-between transmission points have uncorrelated fast-fadingcomponents and a higher number of UE antennas enable the UE to separatethe different independent transmissions. In comparison to LTE thisenable better support for simultaneous transmission from differenttransmission points that might differ in terms of large scale channelcharacteristics.

CSI Acquisition

The CSI acquisition process involves the UE being assigned a CSI-RS fromthe serving node, which is used by the UE to calculate a rank, aprecoder, and the resulting CQI.

CSI-RSs are transmitted according to CSI acquisition demands and only onthe part of the bandwidth where there are current or expected futuredata transmissions; see section 2.3.6.5. The eNB makes the decision whento transmit CSI-RS and when the UE should report. Information on whatCSI-RS resources to measure on are conveyed to the UE over dPDCH. Incase of element based feedback, it is possible to share, to a largerextent, CSI-RSs between UEs, and enable more filtering in comparison tomore dynamic beam-based schemes. An additional potential benefit ofsharing CSI-RS configurations is that the UEs can be more easilyconfigured to rate-match around the common CSI-RS and hence utilizedmore resource elements for data.

FIG. 102 illustrates options of beam shapes for feedback-based solutionsin NX.

3.4.3.2 Beam-Based Feedback

Transmitting in a beam implies that there is a directional, possiblynarrow, propagating stream of energy. The notion of a beam is thusclosely related to the spatial characteristics of the transmission. Toease the discussion, the beam concept is first explained. In particular,the notion of a high-rank beam is described.

Here, a beam is defined as a set of beam weight vectors, where each beamweight vector has a separate antenna port, and all the antenna portshave similar average spatial characteristics. All antenna ports of abeam thus cover the same geographical area. Note, however, that the fastfading characteristics of different antenna ports may be different. Oneantenna port is then mapped to one or several antenna elements, using apossibly dynamic mapping. The number of antenna ports of a beam is therank of the beam.

To illustrate the beam definition, take the most common example of arank-2 beam. Such a beam is realized using an antenna withcross-polarized elements, where all antenna elements with onepolarization are combined using one beam weight vector, and all antennaelements with the other polarization are combined using the same beamweight vector. Each beam weight vector has one antenna port, and sincethe same beam weight vector is used for the two antenna ports, the twobeam weight vectors together constitute one rank-2 beam. This can thenbe extended to beams of higher rank.

Note that high-rank beams may not work for the UE. Due to the irregularantenna element layout, the rich scattering at the UE and the fact thatthe UE antenna elements may have different characteristics, it is verychallenging to construct several beam weight vectors with similarspatial characteristics. Note that this does not preclude spatialmultiplexing in the uplink: this can be achieved using several rank-1beams.

It is very important to note that the beam shapes can be quite flexible.Hence, “beam-based transmission” is not the same as “fixed-beamtransmission”, although using a fixed grid of beams may be a suitableimplementation in many cases. The working assumption is that each beamhas between 1 and 8 ports, and each beam is associated with a CSI-RSwith a rank ranging from 1 to 8.

From UE's point of view, no major difference to element-based feedbackis foreseen other than the CSI-RS configuration; namely, that forbeam-based transmission, the CSI-RS allocations need to be moreflexible. Even though the configuration is flexible this does notpreclude that the UE may do filtering and interpolation, but this isunder strict network control.

Beam-Based Transmission

In beam-based transmission, communication occurs through beams, wherethe number of beams may be much smaller than the number of antennaelements. Since the beams are still adjustable, the antenna system as awhole retains all its degrees of freedom. However, a single UE is notcapable of supporting all these of freedom using instantaneous feedback.Note that this is in contrast to element-based transmission described insection 3.4.3.1, where the UE sees all the degrees of freedom of theantenna, and is capable of reporting based on this knowledge.

From the network's point of view, multiple simultaneous beams can begenerated, either using analog beamforming or digital domain processing;see section 3.4.6.1 for a description of various options for beamformingarchitectures. It is assumed that as long as the formed beams are ofsimilar width as the angular spread of the channel, the overhead tomaintain the UE beam associations are reasonable: the best beam for anysingle UE does not then vary with the fast fading. When the beam isnarrower than the angular spread of the channel, the best beam for anysingle UE varies over time, leading to that the best beam associationneeds to be frequently updated. In some cases, the antenna patterns arefixed; see FIG. 98, option 2. In some cases, the beams are adapted tothe UEs channel characteristics; see FIG. 98, option 3, where user 2with a rich channel receives data through a wide high-rank beam and theLOS user 1 a narrow rank-2 beam.

Beam-based transmission is applicable in both FDD and TDD, for anyfrequency band, and antenna size.

Beam-based uplink reception implies that the baseband does not haveindividual access to all antenna elements. In this case, some sort ofspatial preprocessing or preliminary beamforming may be applied. Thispreprocessing can be performed in the analog domain, in the digitaldomain, or in a hybrid of the two; see section 3.4.6.1. In general, thespatial preprocessing can be quite flexible. It needs to be time-varyingto adapt the coverage area of the antenna to where the users are. Bothphase and amplitude tapering can be considered.

In the downlink, the individual antenna elements are never exposed tothe UE. The UE only sees a number of linear combinations of the signalstransmitted from different antenna elements. The number of linearcombinations that is exposed is determined by the rank of thetransmission. Data is received at the UE through such a linearcombination (the beam) and downlink quality is measured and reported perbeam.

Pre-/Decoding Options and CQI Acquisition

With beam-based transmission, the eNB in principle still has fullflexibility in forming the desired beams, or equivalently using anyprecoding. The way to adjust the precoding is different for FDD and TDD,and it is different for different beamforming architectures. In whatfollows, downlink and uplink procedures are described independently. Inmany cases, reciprocity can and should be used to improve performance ofthe procedures. In the final part of this subsection, reciprocity isexplicitly discussed.

Precoder selection is based on beam-formed CSI-RS (see section 2.3.6.5)that is inserted at specific locations in the time-frequency grid inline with the data. These CSI-RSs are activated on demand, and the eNBdecides through which beam the CSI-RS is transmitted. It is assumed thatwhen scheduled, one CSI-RS uses one resource element. Each CSI-RS may betransmitted in different beam, transparent to the UE. One example of aCSI-RS allocation, where two CSI-RSs are transmitted, is shown in FIG.99.

Both time- and frequency-multiplexing of CSI-RS should be supported, butit should be noted that for beamforming architectures that are not fullydigital, transmitting different CSI-RSs at different points in time usesless baseband hardware than transmitting different CSI-RSs at the sametime in different subcarriers. On the other hand, transmitting severalCSI-RSs in different subcarriers at the same time means that more beamscan be measured at the same time.

To enable link adaptation, one of the CSI-RSs can be transmitted overthe same beam as the currently scheduled data. Other CSI-RSs may betransmitted through other candidate beams, and the selection of thesecandidate precoders is the responsibility of the eNB. Still, this istransparent to the UE; only the eNB knows which CSI-RS is transmittedthrough which beam. For some CSI-RS allocations, observe that if aCSI-RS has high rank and or multiple associated UEs a precoderassumption can be desirable to improve link adaptation accuracy in theMU-MIMO case, both for interference estimation and signal qualityestimation.

The number of CSI-RSs that are required depends on how many candidatebeams need to be probed and also how frequent updates are required. Notethat in many cases, the number of beams that need to be probed may notbe very large. For instance, only two CSI-RSs may be assigned in eachsubframe, and transmitting through different candidate beams insubsequent subframes. To cater for this flexibility, the CSI-RSsallocation can be signaled in the DCI field. Since the CSI-RS istransmitted in line with the data, the amount of payload data needs tobe reduced to make room for the CSI-RS. The amount of overhead variesdepending on how many UEs are active, and the flexibility that isdesired in the CSI-RS mapping.

Closed-loop codebook based precoding over the all the antenna ports of abeam is used, very similar to how it is done in LTE today. The UEmeasures the CSI-RS transmitted on the antenna ports, derives the mostsuitable precoding matrix from the codebook using the CSI-RSmeasurements, and sends an indication of the most suitable precodingmatrix to the eNB. Thus, the antenna port precoder is determined by theUE, based on one high-rank CSI-RS, whereas the beam is selected bycomparing the CQIs reported by the UEs for different candidate beams. Ifa beam has higher rank than 2, the precoders would be of larger size andhence operate also over the spatial domain. As in LTE, the codebook forthe precoder needs to be standardized.

MRS can also be used to select beams, using the procedures described insection 2.5. As CSI-RS uses significantly less resources than MRS,CSI-RS is generally used whenever possible. As a rule of thumb, CSI-RSwould be used within one node. To be more precise, MRS would have to beused when the serving and candidate beams are non-synchronized. Anothersituation where MRS would have to be used is when the user data in thenetwork needs to be rerouted, e.g., when an S1 path data switch isrequired.

When a UE is allocated multiple beams, the UE has been assigned severalCSI-RSs and each CSI-RS has a certain rank. The UE measures on allallocated CSI-RS, and selects the most suitable antenna port precoderfrom the codebook. For each of the CSI-RSs, the UE transmits a precoderindex, a CQI value and a rank indicator.

Upon reception of the CSI report, the eNB maps each CSI report to thebeam it was transmitted in. The eNB chooses the beam for the subsequenttransmissions based on the reported CQI values, and also selects theprecoder based on the suggestion from the UE. The CQI value is also usedto select modulation and coding for the next transmission.

Note that the CSI-RS measurement scheme works also for MU-MIMO.Different UEs are assigned different CSI-RS allocations, as shown in theproposed CSI-RS allocation for MU-MIMO operation shown in FIG. 100. Inthe resource elements where the CSI-RS is transmitted to one user,interference from the data transmissions to the other user is measured,and vice versa. Hence, both measurements reflect the currentinterference properties of the co-scheduled user.

The starting point for the design is that the CSI-RSs are UE-specific,where each UE is assigned a distinct set of CSI-RSs to measure on. Toreap the full benefits of the antenna system, the network also needs totransmit individual CSI-RSs through UE-specific candidate beams. Thismeans that when there are many active UEs in a cell, quite many CSI-RStransmissions are needed. In that case, there may be an option to letseveral users measure on the same CSI-RSs, for example, by mapping theCSI-RS to a grid of beams.

For beamformed uplink reception, there is generally not access to theoutput from all antenna elements. Instead, there is access to a linearcombination of these element signals, and that linear combination canonly be updated based on previously received data.

Also in uplink, the notion of serving and candidate beams is relevant.We assume that the UE is able to successfully maintain communicationwith the network over a certain UL beam. In parallel, the network alsoreceives the UE transmission in one or several candidate beams, and usese.g., the transmitted RRS to estimate the quality in the candidatebeams. These quality measures are then used to update the serving beamfor subsequent transmissions, and also to form new candidate beams inthe future.

The more challenging use case for a beams-based solution is MU-MIMO fortwo users who have strongly correlated channels in spatial domain. Wherethis scenario is handled with feedback mechanisms instead of coherentreciprocity (see section 3.4.3.3) the UEs need to emulate inter-beaminterference. One possible method to achieve MU-MIMO precoder selectionis by configuring the UE with multiple (at least 2) CSI-RS and signalingthe UE with some precoder information for the interfering CSI-RS.Further CSI-IM might still be needed to estimate non-coordinatedinterference.

Much of the complexity in the above procedure lies in how to formrelevant candidate beams. In a possible first implementation, a subsetof a grid-of-beams is used as candidates. Even in this case, thequestion on how to choose this subset intelligently is non-trivial. Inthe absence of any a priori information, the full grid-of-beams may needto be probed, measured and reported. The information about beam qualityshould then be stored at the eNB, and used for subsequent candidate beamselection.

Candidate beam selection may also include beam narrowing. Here,communication may be initially maintained using a rather wide beam, withthat beam then being refined by making it narrower.

It is worth noting that the process described above is based on theassumption that the UE is able to reliably receive a CSI-RS allocation,and to subsequently transmit the resulting measurement. Under thiscondition, it is possible to maintain, update, and refine the beam usedfor communication.

Using Reciprocity with Beam-Based Transmission

As reciprocity is a very powerful property to be used with multi-antennaarrays, it is vital to highlight its usage when combined with beam-basedtransmission.

For TDD deployments, when digital beamforming architecture with adequatecalibration is available at the eNB, it makes sense to use coherentreciprocity to select the precoder used for transmission, at leastcloser to the cell center where coverage of UL signals is good. It thenbecomes possible to use quite powerful precoders, similar to thedescription in section 3.4.3.3. However, we may still transmitbeamformed CSI-RS together with the data, and use that for linkadaptation.

In some cases, coherent reciprocity cannot be used, and weakerreciprocity relied on instead; see section 3.4.2. This includes caseswith digital beamforming in FDD deployments. Using coherent reciprocitywith hybrid beamforming can be tricky, since there is only access to theuplink channel over the receive beams.

For calibrated analog and hybrid beamforming, measurements on DLcandidate beams can be used to choose UL candidate beams, and viceversa. In fact, measurements on DL candidate beams may be used todirectly select UL serving beam and vice versa. This is possible both inTDD and FDD.

3.4.3.3 Coherent Reciprocity-Based Massive MIMO

This is the most forward-looking multi-antenna technique in NX, havingthe highest performance potential for dedicated data transmission andreception. It constitutes a special case in the general class oflarge-scale individually-steerable antenna systems, also known asmassive MIMO. A first distinguishing factor is that it relies on thestrictest, so-called “coherent”, form of reciprocity, achievable only inTDD, in which the RX and TX channels are the same within the coherencetime/bandwidth interval. Explicit instantaneous CSI is obtained byuplink measurements and it is used both for uplink and downlinkbeamforming design, enabling full exploitation of the angular spread.

A second distinguishing factor is that, in order to realize theperformance potential, a fully-digital implementation is assumed (seesection 3.4.6.1) that allows element-based, flexible, array processing.Due to the many degrees of freedom that can be used for interferencesuppression, flexible beamforming can in principle enable high-orderMU-MIMO operation. Hence, this mode is particularly suited forincreasing the capacity in crowded scenarios with low mobility and goodcoverage, without need of strong LoS component.

For many relevant scenarios, with low angular spread or limited chancesfor MU-MIMO, massive MIMO processing can be performed in the angulardomain, assuming some sort of preprocessing (e.g., by a grid-of-beams),taking into account the tradeoffs among (HW, computational, CSIacquisition) complexity and performance.

Element-Based Precoding Options

Candidate flexible precoding schemes, relying on explicit knowledge ofthe instantaneous channel matrix, that are being considered in NX aremaximum ratio transmission (MRT), zero-forcing (ZF), andsignal-to-leakage-and-noise ratio (SLNR) precoding. MRT is the simplestand robust method but cannot null interference. This can be achieved byZF, but this is more computationally complex and sensitive to channelestimation errors. SLNR is a mixture of MRT and ZF, where the mix ratiocan be controlled by a regularization parameter; SLNR is equivalent toMMSE for equal power allocation. For an increasing number of antennaelements, the performance of MRT approaches that of ZF since the channelvectors of different UEs gradually become close to mutually orthogonal.

Conventional flexible precoding solutions are derived assuming aconstraint on the sum power of all PAs. This typically results inprecoding weights having different amplitudes for different antennaswhich in turn imply that not all PAs are fully utilized. Even though thepower per PA in a massive MIMO system is expected to be in the order ofmilliwatts, this may still be an issue in the situation where thecoverage of the beam should be maximized without over-dimensioning (onthe average) the PAs. Taking this power loss into account may translateto a significant performance loss. An ad hoc solution to the problem isto simply use only the phase of the conventional precoder solution. Thiscan in some cases be good enough. A more rigorous approach is to takethe per-antenna power constraint into account in the derivation of theoptimal precoder, but this problem is difficult to solve analytically.

A feature of coherent reciprocity-based massive MIMO is that, due tochannel hardening, the benefits of channel-dependent scheduling diminishwith the number of eNB elements. Channel hardening has been validated insingle cell setup, but the diminishing returns have been only partlyvalidated for single-user scheduling. It is expected that channelhardening simplifies scheduling and/or link adaptation, but most likelygains even out due to the complicated user grouping for MU-MIMO. Notethat frequency multiplexing of users is still a relevant feature.

There are a number of issues that need to be developed before any givenimplementation of coherent reciprocity-based massive MIMO is put intouse, for example:

-   -   Computational complexity, data buffering and shuffling;    -   Multi-user scheduling and link adaptation;    -   Effect of angular-domain preprocessing;    -   Performance in different deployments, use cases, traffic        patterns, frequencies, etc.

CSI Acquisition

CSI acquisition at the eNB serves the purpose of enabling coherentdemodulation of uplink data as well as, assuming that adequate coherencyexists, precoder selection for DL data transmission. CSI acquisition isalso used to support frequency-selective scheduling and link adaptation.

As interference is not reciprocal, the procedure is complemented by afeedback mechanism that enables a UE to report local interferenceestimation/measurement to its serving eNB. This interference measurementby the UE can be supported by DL RSs that are similar to CSI-RS andinterference measurement reference signals (IMR) that are similar toCSI-IM in LTE.

CSI acquisition is based on the UL transmission of a new RS, tentativelycalled reciprocity RS (RRS), whose functionality and properties aredescribed in section 2.3.7.3. RRS provides similar functionality as theSRS and DMRS in LTE. A difference is that RRS is flexibly allocated bothin frequency and time, depending on the functionality they provide andthe size of the coherence interval. Also, even though RRS are used fordemodulation, its transmissions are decoupled from UL datatransmissions. In fact, this decoupling is in line with the lean designprinciple of transmitting RSs only when needed. With RRS, the RStransmission is based on the channel coherence time and bandwidth andthe actual need to update its current CSI information rather thanconnecting RS transmissions to data transmissions as with legacy ULDMRS. The subframe types for beam-based feedback and coherentreciprocity-based modes are compared in FIG. 101.

The RRS design allows a UE to be configured with a set of RRSs that canbe flexibly configured by MAC; see section 2.2. To support CSIacquisition for UEs with different coherence bandwidth, coherence time,UL/DL traffic pattern, bandwidth and antenna capability, the RRS isconfigured by a number of parameters that are similar to the SRSparameters in LTE. Both periodic and aperiodic RRS transmissions arepossible. To keep the RRS overhead at a low level but to ensure reliableCSI acquisition, the eNB can trigger RRS dynamically and turn on/offperiodic RRS transmission.

Reciprocity-based CSI acquisition imposes constraints on, for example,using different antennas for RX and TX, different numbers of antennasfor RX and TX, UE beamforming, channel aging, interference, etc. Thesystem thus needs to be carefully designed to achieve coherentreciprocity.

For multiple antenna UEs, RRS precoding is also supported; see section3.4.4.2. If precoding is used for data, then RRS also needs to beprecoded for demodulation. But RRS used only for DL precoder selectionshould not be precoded, or, at least, the rank of the RRS transmissionshould have the same rank expected for the DL. The rank is controlled bythe network by explicit signaling and assigning multiple RRS sequencesto the UE. When both the UE and the eNB rely on reciprocity (see section3.4.4.3) there is a risk for a “dead-lock” situation, sticking to alocal max instead of a global, in the beamforming process. RS with wideangular coverage transmitted from both UE and eNB may solve this.

To manage pilot contamination as well as to configure the IMRs, massiveMIMO operation benefits from some level of multicell coordination. Atthe minimum, within the sectors/cells comprising a cluster orthogonalRRS can be assigned to avoid pilot contamination.

3.4.4 Multi-Antenna UE Transmission

In this section, multi-antenna UE aspects, mainly related totransmission, are given. In general, UEs in NX can be very differentdevices. For instance, when NX is used for wireless backhaul, themulti-antenna properties of the UE in the backhaul link are very similarto those of an eNB. Also, UE devices for V2X applications may be quitedifferent compared to smartphones and tablets. Here in, the focus isstill on a handheld device, such as a smartphone or a tablet, as this isbelieved to be the most challenging case.

Three possible modes are described for UE precoding, in analogy withsection 3.4.3.

The angular coverage of individual antenna elements decreases at higherfrequencies, as compared to currently used frequencies, due to the factthat the elements become smaller in comparison to the size of a device,which leads to an increased interaction between the element and the restof the device. From measurements, it has also been observed that bodylosses seem to decrease at higher frequencies. As a consequence, it isexpected that the element gain increases.

The orientation of a device is many times unknown in relation to thedirection of the eNB (or rather the signal paths). For this reason, itis desired to have an antenna system with more or less “omnidirectional”coverage. Taking the limited coverage per element in consideration, thisimposes the need for multiple elements arranged to cover differentspatial directions and polarizations. Obviously it cannot be generallyassumed that the multiple antennas on a UE are arranged in a uniformlinear array (ULA) or uniform rectangular array (URA), as is often thecase at the eNB. It cannot even be assumed that the elements are closelyspaced or that they are identical.

For a UE with multiple elements, beamforming gains are expected. Howlarge the gains are depends on several factors, such as the number ofantennas, channel knowledge, and precoder design. For example, gains inthe order of 6-7 dB over an “ideal” isotropic antenna have been foundfor an array of 8 elements in uplink using a precoder with phase-onlytapering. To be noted is that this value only includes beamforminggains; any gains due to reduced body losses are not included. Simplerprecoders such as antenna selection, which are feasible since eachelement is directive and thus offers a few dB antenna gain, suffersignificantly in UL given there is one power amplifier per antenna andthus the total output power is reduced significantly.

3.4.4.1 Element-Based Feedback

With element-based feedback, reciprocity is not used. Instead, thechannel between each UE antenna element and the eNB is observed via RSstransmitted from each UE antenna. RRS is one possible RS, butpotentially an uplink CSI-RS can be considered as well. The eNB receivesthe RSs, applies all possible precoders, derives a suitable receiver,and estimates the resulting quality for the different precoder optionsat the receiver output. The result is fed back to the UE, most probablyin terms of a PMI, RI, and resulting CQI over dPDCH, in combination witha scheduling grant.

For an element-based feedback solution, a fully digital implementationis practical, where each element is reached by the baseband on bothreceive and transmit. The radiation properties for each element arefixed.

In contrast to codebooks used at the eNB, precoder alternatives, due toUE antenna topologies, may also include cases where only one or a fewantennas are used; the patterns of the individual antenna elements areprobably different, especially at high frequencies. The UE strictlyfollows the instructions from the eNB, and applies the selectedprecoder; this is similar to the LTE uplink.

As the uplink transmission is based on feedback from the eNB, it is thusagnostic to TDD or FDD. Furthermore, there is fundamentally no need forcoherency in between TX or RX chains, nor between RX and TX pathsconnected to the same element.

3.4.4.2 Beam-Based Feedback

The scenario here is that the UE is equipped with multiple arrays, eacharray consisting of a (small) number of elements. The different arrayscover different spatial directions. The array can be configured to havedifferent angular coverage (pointing direction and beam width).

The UE transmits RSs through a number of beams, either sequentially orsimultaneously. Sequential transmission can be used also with analog TXbeamforming, and the detection at the eNB is easier. On the other hand,if RSs are transmitted over several beams in parallel, more beams can beprobed in a shorter time. The RS is probably RRS, as different RSsshould be transmitted through different beams, so that the eNB canidentify each transmission. The shape of each beam is decided by the UE,but the number of beams is between the UE and the eNB. The eNB measuresthe quality of each received RS, and determines the most suitable UEtransmit beam. The decision is then sent to the UE over dPDCH, togetherwith a CQI value and a scheduling grant.

As mentioned in section 3.4.3.2, it may not be possible to form ahigh-rank beam at the UE. To enable uplink MIMO, several rank-1 beamsmay be used.

At the eNB, beam-based transmission typically means that the number ofelements seen by the baseband is much lower than the number of elementsused to form the beams. This implies that the (angular) coverage ofsimultaneous individual beams is less than by the elements.

At the UE, beam-based transmission for feedback purposes may be used toimprove link budget for RSs but perhaps not to reduce the angularcoverage, such that the number of beams may still be equal to the numberof elements.

For an ongoing transmission there is a possibility to reduce the angularcoverage, as is done on the eNB side, but this may imply that, aftersome time, the channel is not fully utilized. To prevent this, sounding,with wide or possibly full angular coverage, is required.

3.4.4.3 Reciprocity-Based

The scenario here is that each antenna at the UE is equipped with a pairof RX/TX chains and that any differences in amplitude and phaseresponses are known to an adequate level, either by calibration ordesign. Hence, coherent reciprocity is assumed. The weaker types ofreciprocity (see section 3.4.2) that typically are suitable for FDD atthe eNB side, may not work so well at the UE side, in case thetransmission involves multiple elements with fairly large, possiblyuncertain relative positions and different element types. The reason isthat the transformation of precoders from receive to transmit carrierfrequency, which may be needed depending on relative carrier separation,may introduce significant errors.

Channel matrix is estimated on downlink RSs, which can be DMRS or, incase of no data transmission in downlink, CSI-RS. How many CSI-RS needto be allocated depends on what transmission scheme is used in downlink.When beam-based or reciprocity-based transmission is applied in thedownlink, a small number of CSI-RS is enough. For element-based downlinktransmission, one CSI-RS per antenna element may be required, leading toa large overhead.

On the eNB, there are several well-known precoder design principles,e.g., MRT and ZF (see section 3.4.3.3). Similar approaches can beenvisioned also at the UE side. However, one or more of the followingadditional aspects may also be considered:

-   -   Power utilization becomes more important, as the UE is typically        power limited. Using precoders that result in that no or very        little power is transmitted from some of the PAs may not be a        good idea. This situation may be quite common at the UE, since        the directive antenna elements are pointing in different        directions, and may be of different types.    -   The CSI estimated from DL transmission may be outdated more        quickly than at the eNB, due to the rich scattering environment.        Hence, a more robust precoder design may be applicable.    -   EMF requirements are stricter at the UE side. Additional        considerations should be taken to ensure that all regulations        are fulfilled.

3.4.5 Multi-Antenna Aspects of Other Procedures

In this section, multi-antenna aspects of other procedures thandedicated data transmission are raised.

Note that the case where NX is operating stand-alone is considered here.When NX is tightly integrated with LTE, some of the procedures can beexecuted over LTE. This is true in particular for the provisioning ofsystem information, described in section 3.4.5.1, for the standalonecase. If the RRC connection establishment is done in LTE, the UE wouldend up in NX CONNECTED ACTIVE state. Note that the working assumption isto use the random access procedure described in section 3.2.2 to getfrom NX CONNECTED DORMANT to NX CONNECTED ACTIVE.

3.4.5.1 System Information Provisioning

The signature sequence (SS) defined in section 2.3.6.1 is used to conveythe signature sequence index (SSI) and provide coarse time sync and forUL power control of random access transmission. It is advantageous forthe SS transmission not to rely on beamforming, since it needs to betransmitted over a large coverage area, and in many cases, this ispossible since the amount of information that needs to be transmitted isenvisioned to be quite small. However, in challenging coveragescenarios, the SS coverage may be insufficient. In this case, the SS canbe transmitted in a narrow beam, whose pointing direction can be swept,so that the whole area is covered.

SSIs can be transmitted using beamforming in different ways. Forexample, different SSIs can be allocated to different beams or SSI reusefor multiple beams can also be considered. This affects the way the RACHpreamble detection is performed.

The SSI is used as an index into the AIT. When the AIT is delivered tothe UE over NX, it is anticipated that beamforming is not required.Instead, coding and repetition is applied to achieve the desired levelof reliability.

3.4.5.2 Random Access Procedure

The random access procedure is defined and described in detail insection 3.2.5.2, whereas the focus in this section is the relatedmulti-antenna aspects. What is important in this context is that the UEinitiates a procedure to setup a connection with the network, and thenetwork has no knowledge of the UE location or the beam most suitablefor transmission and/or reception.

As the network (or the UE) has no knowledge about the UE location orbest beam, it is usually not possible to utilize the maximum antennagain when transmitting and receiving the messages during random access.This is true in particular for analog beamforming at the eNB and the UE.However, the amount of data that needs to be transmitted is quite smallfor all the messages in the random access procedure, when compared tothe data rates that NX is expected to deliver. Hence, the SINR requiredto receive the initial setup messages is deemed to be significantlylower, compared to the SINR required for data transmission.

The UE initiates the process by sending a PRACH preamble, described insection 2.3.7.1. The most common case is that no UE TX BF is required,due to the low SINR requirements of the PRACH. If UE TX BF is required,it may be possible to utilize reciprocity to transmit the PRACH fromwhere the SS was received. Note that in this case, it is very likelythat only nodes that transmit SS receive PRACH. Also note thatreciprocity is difficult to use when SFN transmission is utilized for SStransmission. When reciprocity cannot be utilized, the UE can repeat thePRACH preamble transmission at subsequent transmission opportunitiesusing different TX beams. Hence, the procedure is not optimized for thatcase, but the increased access delay is simply accepted where coverageis bad. Note that the UE does not have to use the narrowest beam wheninitiating the transmission, but may rely on a wider beam. The eNBlistens for PRACH preambles in the allocated time slots. The networkdetects which PRACH was transmitted and at the same time estimates thespatial properties of the received signal. These spatial properties arethen used to transmit the random access response.

When the SS is transmitted in a narrow beam, which is swept over thecoverage area, spatial signature estimation may be unnecessary. Instead,it may be advantageous to indicate different SSIs in different beams,and let different SSIs point to different PRACH preambles. With thissetup, the network can deduct which was the best downlink beam bychecking the received preamble, and use that info for subsequentdownlink transmissions.

For a digital eNB beamforming solution using element-based uplinkreception, the spatial properties of the received signal are estimatedin baseband. In this case, it becomes feasible to use the full arraygain, and no uplink coverage loss occurs. In a TDD system, coherentreciprocity could be used, whereas in an FDD system, the spatialsignature needs to be mapped to an angle-of-arrival (AoA) and thenmapped back to a suitable beam for transmission. Such a remapping worksonly for closely spaced antenna elements. Note that we may considerantenna architectures where the digital beamforming is only done over anarrow frequency range, corresponding to the PRACH bandwidth.

For hybrid beamforming architectures (see section 3.4.6.1), thesituation is different. Two solutions can be envisioned:

-   -   1 Some coverage loss relative to the full antenna gain occurs.        This coverage loss is related to the relation between the number        of antenna elements and the number of digital receiver chains.        Basically, each receiver chain is attached to different,        non-overlapping receive beams, and together, these broad beams        cover the area from which the PRACH may be received. In effect,        the PRACH coverage is n_(ant)/n_(TRX) worse than the maximum        PDCH coverage. For instance, with 8 TRXs and 64 antennas, this        corresponds to 9 dB. This needs to be accounted for in the        dimensioning, but for many cases, PRACH coverage is not        limiting. In this case, the spatial signature can be estimated        from the combined outputs of the receive chains.    -   2 For cases with very large antenna arrays and/or very few        receiver chains, the PRACH coverage is good enough if the        previous procedure is used. The PRACH coverage may then be        limiting performance, especially if we dimension for low uplink        data rates. Basically, a higher antenna gain is desirable to be        able to receive the PRACH. Here the receive beamformer is swept,        while the UE repeats the PRACH transmission.

In what follows, it is assumed that the PRACH can be detected, and thata spatial signature, or a suitable downlink beam, can be established.

After having detected the PRACH, the eNB uses the AoA estimated from thePRACH transmission to form a beam to transmit the random access response(RAR), see section 3.2.5.2. The width of this beam is determined by thequality of the AoA estimation from the PRACH reception. The width of thebeam can be controlled using the methods described in section 3.4.5.6,if necessary in the analog domain.

The UE receives msg2 and transmits msg3 over PDCH. The eNB receives msg3using the information from the PRACH reception to improve reception andto refine the AoA estimate. Assuming that the AoA estimated from thePRACH is good enough, the reception of msg3 works for both digital andanalog/hybrid beamforming. With the refined AoA estimate, msg4 can betransmitted in a quite narrow beam.

The procedure above sequentially improves the beam selection using thetransmitted signals. Once a good enough beam is established so thatcommunication maintained, the procedures in section 3.4.3 are used torefine the beam. In some cases, msg2 and msg4 can be transmitted withoutany beam refinement.

3.4.5.3 Beamfinding

The use of beamforming in NX affects procedures for establishing a newlink between the UE and the network. When data transmission employsbeamforming, the link establishment includes determining the preferredtransmission beam configuration, in addition to the traditionalsynchronization tasks.

Some examples of such procedures are switching to another set of nodese.g., when changing the network layer (the current serving beam may thenbe irrelevant) or first access in a new frequency band (the spatialproperties of the new and previous bands may differ significantly). Whenthe UE has an established link to the network, at some node layer atsome frequency, beam finding towards another layer or frequency isinitiated by the network and typically handled as an active modeprocedure. DL beam finding is based on providing a set of candidatebeams in the DL for the UE to measure quality and report back to thenetwork. The network configures the measurement and reporting modes,issues a measurement command to the UE, and turns on the MRS in relevantbeams; see section 2.5.3. The MRS in the different beams are transmittedusing beam sweeps in time, frequency, or code space, where the sweep maycover the full range of beam directions, or a reduced subset if usableprior info is available. The common MRS measurement configurationframework is used. UE reports after MRS measurements are then used todetermine the first serving beam at the new layer/frequency.

In initial system access scenarios where no prior UE info and beamdirection information is available, beam finding may be applied formaking the random access procedure more efficient, or in some cases,possible. While control signaling does not typically require the samedegree of beam refinement as high-performance data transmission, it isexpected that some beam forming is required at higher frequency bands toreceive system information and complete the RA procedure; see section3.2.5.2. The SSI design includes beam sweeping mechanisms andidentifications for the different DL beam configurations; see section2.3.6.1. The UE reports back the best received option in the UL RApreamble. This beam finding info is then used by the responding node todirect the RAR and subsequent signaling in the direction of the UE.

3.4.5.4 Active Mode Mobility

The AMM solution in NX, described in section 3.5, is configured tomanage mobility between beams, as opposed to the traditional cellmobility in LTE. Beam-oriented transmission and mobility introducenumerous features that differ from LTE cell mobility. Using large planarantenna arrays at access nodes, with the number of elements in thehundreds, fairly regular grid-of-beams coverage patterns with hundredsof candidate beams per node may be created. The beam widths of theindividual beams in elevation and azimuth are determined by the numberof element rows and columns in the array.

As illustrated in simulation studies, the coverage area of an individualbeam from such array may be small, down to the order of some tens ofmeters in width. Channel quality degradation outside the current servingbeam area is rapid, which may necessitate frequent beam switching toreap the full potential of the antenna array with low overhead. Staticmobility signals in all beams are not feasible, so MRS need to be turnedon only in relevant beams and only when needed; see section 3.5.3. Therelevant beams are selected based on the UE position and prior beamcoverage statistics for the different candidate beams, based on a SONdatabase; see section 3.9.4. The SON data may also be used to triggermobility measurement sessions when the serving beam quality degrades,without the need for continuous neighbor beam quality comparisons.

Evaluations indicate also that sudden beam loss is possible due toshadow fading, e.g., when turning a street corner. The AMM solutionincludes features that assist in avoiding or rapidly recovering from asudden link quality reduction or out-of-synch condition; see section3.5.6.

The AMM solution is presented in detail in section 3.5. This includesboth lower-layer procedures (mobility trigger, measurements, beamselection, RS design, and robustness) and RRC topics (beam identitymanagement, inter-node HO, and other higher-layer aspects).

The AMM solution described in section 3.5 supports both beam switcheswithin one node and between different nodes using primarily measurementson MRS. Note that the procedures described in this section can be usedto change beams within one node using measurements on CSI-RS. Or to bemore precise: beam-switches using CSI-RS can be used for cases when thedata plane does not have to be re-routed, and no resynchronization needsto be done. On these cases, the CSI-RS-based procedure is much leaner,and is also completely transparent to the UE.

Furthermore, the AMM solution distinguishes between link beams andmobility beams. Link beams are the beams used for data transmission,whereas mobility beams are used for mobility purposes. Hence, almost allthe beams discussed in this chapter are link beams; the mobility beamsare only described in this very subsection.

3.4.5.5 Multi-Antenna Functionality for Inactive UEs

In section 3.4.3 the multi-antenna procedures for dedicated datatransmission are described. The description focuses on the case whendata is continuously transmitted. However, packet data transmission isbursty by nature. Many packets are actually quite small, and idleperiods between packets are common and of unknown and varying length. Itis crucial that the multi-antenna functionality can handle this type oftraffic patterns efficiently. A UE is moved to dormant state when nopackets have been transmitted or received for some time. The workingassumption is that the network loses all beam related information whenthis happens, and that the random access procedure described in section3.4.5.1 is used to return to active state.

However, there is a time period between when the data transmission endsand the UE is moved to dormant. During this period, the UE appliesmicro-DRX, and it should be possible for the UE to resume datatransmission or reception very quickly. This means that the networkshould maintain some notion of a suitable beam to use for datatransmission. Reasonably accurate time-frequency sync should also bemaintained, as well as an up-to-date node association.

For element-based transmission, it is assumed that transmissions ofdownlink reference signals continue also during idle periods. Asmentioned in section 3.4.3.1, the different UEs may share the samepilots, so the amount of resources used for this RS transmission islimited irrespective of the number of UEs. Also, it may not be necessaryto maintain the full bandwidth of the RS transmission.

For beam-based transmission, the situation is more complicated, sincethe RS are in general UE-specific. To maintain a suitable beam, thenetwork and UE can rely on some sort of RSs. This may be done by havingthe UE measure quality on a set of downlink signals corresponding todifferent beams, and report the beam quality to the network, eitherperiodically or in an event driven fashion. The downlink RSs that havebeen previously described are CSI-RS and MRS. Here the same principle asfor data transmission is applied: use CSI-RS for intra-node beamswitches, and activate MRSs from neighbor nodes when no intra-cellcandidates are good enough.

The number of UEs that are simultaneously transmitting or receiving datais rather small. However, the number of UEs that are in the active statebut not transmitting/receiving can be rather large. As MRSs are onlyactivated when there are no good-enough intra-cell candidates, thenumber of MRSs is not a bottleneck. However, the CSI-RSs are transmittedperiodically to estimate the quality of intra-node beams and with manyUEs in active mode, the amount of CSI-RSs that need to be transmittedcan be quite large.

To reduce the CSI-RS resource consumption, one or more of severalmethods can be applied:

-   -   Transmit the CSI-RS more seldom;    -   Transmit only low-rank CSI-RS;    -   Transmit CSI-RS only over part of the bandwidth;    -   Use wider candidate beams;    -   Allow UEs to share CSI-RSs.        When combined, these methods should make it possible to maintain        quite many UEs in active mode, and to return to high-rate data        transmission rather quickly.

For coherent reciprocity-based massive MIMO transmission, it is assumedthat the network schedules transmission of RRSs with a suitablefrequency to support a quick return to data transfer.

3.4.5.6 Variable Beam Width

Active antenna arrays such as ULAs and URAs offer many degrees offreedom to adapt beam patterns to channel conditions and schedulingneeds. One typical beam example from a large antenna array is a narrowbeam with high gain, possibly with extra low gain in selected directionsfor reduced interference spreading.

Such a narrow beam pattern may be typical for user data transmission (aselaborated in section 3.4.3) whereas other types of transmission, suchas broadcasting of control information or when CSI is less reliable,sometimes require a wider beam pattern. By proper selection of precodersone can, for many array sizes, generate beams for which the beamwidthcan range from very wide, similar to the element pattern, to verynarrow. In many cases the precoding may be done by phase taper only,which is important for active antenna arrays since the total outputpower is given by the aggregated power from all power amplifiers and forpure phase taper the entire available power is used. The EIRP is lowerfor wider beams since the antenna gain decreases. This type ofbeamforming can be applied to linear as well as rectangular arrays, andindependently per antenna dimension. The wider beam can, similar to thenarrow beams, be steered in any direction.

The technique can be used to generate, for example, a beam withidentical power pattern and orthogonal polarization in all directions,as well as beams using more ports, either arranged in one or twodimensions).

3.4.6 Hardware Aspects 3.4.6.1 Multi-Antenna Architectures“Full-Dimension” Digital Beamforming

Ideally, the signals from/to all antenna elements should be digitallyprocessed in the baseband domain so that all the degrees of freedom areavailable (“full-dimension” digital beamforming), as illustrated in FIG.102 for the transmitting side. This gives total flexibility in thespatial and frequency domains for post-processing signals at receptionand for precoding at transmission; thus, enabling full potential ofmassive MIMO features such as frequency-selective precoding and MU-MIMO.

FIG. 102 illustrates a simplified digital precoding-capable antennaarchitecture. For more antennas, the requirements on each radio chaincan be relaxed, see section 3.4.6.2. Using a very large number ofantenna elements (first NX macro eNBs operating at ˜4 GHz are expectedto have 64 elements, with one complete radio chain each (FFT, DAC/ADC,PA, etc.) being a radical change in building practices. Thisnecessitates innovative design to keep in reasonable levels the cost,complexity, and power consumption.

Other practical limitations appear: the baseband unit (BU) can performlimited real-time computations (e.g., inverting 64×64 matrices at highrates may not be practical). Also, the data-rate of the radio interfacebetween the radio unit (RU) and BU is limited and scales very poorlywith the number of antenna elements (for a rough idea, it is seenreasonable to have about 30 Gbps between RU and BU, which can translateto about 8 streams of 20-bits I/O data over 200 MHz).

Active Antenna Systems: Moving Processing from BU to RU

To decrease the bandwidth requirements between the BU and RU, someprocessing can be placed directly in the RU. For instance, the A/Dconversion and the time to frequency FFT conversion can be done in theRU, so that only frequency-domain coefficients are required to be sentthrough the radio interface, which can also reduce the necessarybandwidth. Some digital beamforming may also be included in the RU. Thisis illustrated in the example receiver shown in FIG. 102, for the uplinkreceiver case.

In the uplink receiver case, to further reduce the radio interfacerequirements, the number of streams can be reduced with preprocessing atthe RU. The goal of this preprocessing is to map the dimension of theantenna elements into the dimension of “useful” streams that areprocessed by the BU. This may be done “blindly” e.g., based on pureenergy detection in either in time or frequency domain (before or afterthe OFDM FFT), using DFT-based or SVD-based dimension decomposition andselecting the best dimensions for further processing; or may be donewith assistance of the BU and results of the channel estimations.

In the downlink transmitter case, similar chain of processing can bedone in the reverse order, although the precoding/beamforming commandshave to be sent on the radio interface. The transmitter and receiver mayhave the same number of antenna elements, or they may have a differentnumber of antenna elements.

Hybrid Analog-Digital Beamforming

Another solution that partly enables the benefits of large antennaarrays, while considering practical hardware limitations and havingpromising trade-offs, is the hybrid antenna architecture illustrated inFIG. 104. This usually comprises a two-stage beamforming where onedigital stage is used for individual data streams (closer to thebase-band) and another beamforming stage is made closer to the antennaelements to “shape” beams in the spatial domain. This second stage canhave various implementations, but is usually based on analogbeamforming.

Analog Beamforming

Analog beamforming is done in the analog (time) domain, after the DAC,for precoding. Analog beamforming is therefore frequency independent, inthat it applies to the entire spectrum, and can be done directly in theRU.

FIG. 105 illustrates a simplified analog precoding capable antennaarchitecture. Analog beamforming implementations usually rely onpredefined grid of beams that can be selected to transmit/received datastreams, as illustrated in FIG. 105. Each beam corresponds to aphase-shifting precoder, which avoids having to control the amplitude asthis would require additional PA. Beams can be set to form sectors,hotspots, or some spatial separations to allow user multiplexing.Antenna arrays spanning over 2 dimensions can perform both vertical andhorizontal beam shaping.

Depending on the implementation, all or only parts of the elements canbe used to form the analog beams. Using only a subset of the elementsmakes the implementation easier by having each beam formed by dedicatedelements and thus avoids the issues of “analog summation” of signals.This however reduces the aperture of the antenna and in turn the beamgain. The selection of the beam to use for each stream has to be donewith digital commands. It is currently assumed (to be confirmed) thatthe analog phase shifters can change the beam direction within a CP time(e.g., one or few μs). For shorter CP-durations, especially for thehigher sub-carrier spacing, this could be an optimistic assumption. Arelated issue is how frequently one can actually command the switch tobe done (e.g., once per TTI or symbol, depending on the interface . . .).

3.4.6.2 HW Impairment and Scaling Laws

Much of the feasibility of using very large antenna systems is dictatedby the required hardware quality. For example, to achieve coherentreciprocity (see section 3.4.2), requirements need to be specified. Ifstringent requirements are imposed on a per-antenna basis, the overallcost in terms of power consumption suffers as a result. However, withincreasing array sizes, opportunities for reducing complexity and powerconsumption follow. Some trade-offs are discussed below. Much of thetrade-offs are dependent on the channel or pre-coding conditions sincethis effects the (spatial) correlation between transmit/receive signals.

Data-Converters

To approach a fully digital, large antenna array, potentially largepower savings can be reaped by reducing the data-converter resolution ona per-antenna port basis. This has been shown for the down-link, forseveral different array sizes. 1-bit quantization has also successfullybeen used in the uplink to recover high-order modulation formats in amulti-user massive MIMO setting. When the channel-vectors becomes highlycorrelated, as in a LoS case for example, it becomes impossible toresolve multiple users and higher order modulation. For the UL,resolving the near/far issue is still remaining, which may hamper theuse of low-resolution converters.

Non-Linear, Efficient Power-Amplifiers and Mutual Coupling

Amplifier linearity and efficiency are flagged as important issues fortwo reasons, the first of which is the increased carrier bandwidth andcarrier aggregation, which limits the linearization bandwidth availableto perform correction for the non-linear transfer function of the poweramplifiers. The second is the impact of mutual coupling, as dense,highly integrated arrays may reduce the isolation between branches. Bothof these issues may result in a need for relaxing the linearityperformance on a per-antenna basis, while keeping the performance upover the air.

The out of band radiation and its spatial properties have been studied.In a LoS channel, the gain-curve of out of band radiation follows thatof the in-band, but with some attenuation. Thus, the worst case of outof band interference radiated may be found at the intended user ratherthan a potential victim user. For MU-MIMO over a NLoS channel (IIDRayleigh), the eigenvalue distribution of the transmit covariance matrixwas studied in order to understand the spatial behavior of the out ofband radiation. It was seen that for the multi-user case (10 UEs), thedistribution of the power in the adjacent channel is spread in anomnidirectional fashion. For the single-user case, however, theradiation is beamformed toward the intended user.

Oscillator Phase-Noise

As operating frequency increases, deterioration in terms of phase-noiseoften follows. For a multi-antenna architecture this may have differenteffects depending on the oscillator distribution and/or synchronization.The wave-form specific issues (such as sub-carrier interference due toloss of orthogonality) following increased phase-noise are well knownand left out here.

A challenge for large multi-antenna systems which follows is thedistribution and/or synchronization of local oscillators (LO) in largeantenna arrays which need phase-coherent RF in order to perform eitherbeamforming or multi-user pre-coding. Taking a simplified approach, theimpact of phase-noise and LO-synchronization can be modeled as a powerloss at the receiving user. This in turn manifests itself as decreasedSINR, causing performance degeneration as the ratio between signal andinterference decreases. For multi-user pre-coding the performance lossdepends on the relation between the phase-noise profile and channelcoherence time. In the case of short coherence time, the impact of thelow-frequency phase-noise is reduced.

Simulations show that for the case of independently free-runningoscillators, all power is lost after a certain delay that depends on thephase-noise innovation or LO quality. For the case of low- orintermediate-frequency synchronization, the received power loss islimited only by the frequency stability of the LO's, whereas the powerloss is finite even asymptotically.

Centralized or Distributed Processing

In order to fully utilize the large number of degrees of freedomintroduced with the increasingly large antenna arrays, the radio signalprocessing performed likely needs to take an array-centric perspectivethrough vector signal processing in order to fully use the availabledegrees of freedom. This stretches not only over multi-user pre-coding,but also into areas such as digital pre-distortion, crest factorreduction, etc.

3.5 Mobility

The NX system should provide seamless service experience to users thatare moving, and is designed to support seamless mobility with minimaluse of resources. In this section, the NX mobility is described. Asmentioned in section 1.2, there is dormant mode and active mode in NX,which means that the mobility includes the dormant mode mobility andactive mode mobility. The mobility in dormant mode (location update andpaging) can be found in section 3.2. In this section, only the intra-NXactive mode mobility is treated. Multi-point connectivity and relatedarchitecture aspects are discussed in section 3.12. The description ofreference signals used for mobility procedures can be found in section2.3.6. How to maintain beam neighbor lists is discussed in section 3.8.

3.5.1 Requirement and Design Principles

There are some specific needs that the mobility solution shouldpreferably fulfill, which include one or more of:

-   -   The mobility solutions shall support movement between beams        without any packet loss. (In LTE packet forwarding is used—some        temporary extra delay is OK but loss of packets is not.)    -   The mobility solution shall support multi-connectivity, where        coordination features usable for nodes connected both via        excellent backhaul (e.g., dedicated fiber) as well as via        relaxed backhaul (e.g., latency of 10 ms and above, wired,        wireless).    -   The mobility solutions should work for both analog beamforming        and digital beamforming.    -   Mobility and UE measurements shall work for both synchronized        and unsynchronized ANs.    -   The mobility solutions shall support radio link failure        detection and recovery actions by the UE. The mobility solutions        shall support movement between NX and all existing RATs with a        tighter integration between NX and LTE with short inter-RAT        handover interruption time.

Desirable design principles for active mode mobility include one or moreof:

-   -   A mobility framework built of configurable functions shall be        used.    -   Mobility solutions shall have the flexibility that the DL and UL        mobility can be triggered and executed independent to each        other.    -   For active mode, mobility solutions shall be network controlled        as a general rule, network configured UE control can be used to        the extent there are proven large gains.    -   Mobility-related signalling shall follow the ultra-lean        principle. Preferably it shall occur on-demand, to minimize        measurement signal transmission. The signaling overhead and        measurement overhead related to mobility should be minimized.    -   The mobility solutions shall always maintain a good-enough link        between the terminal and the network (which is different from        “always be on the best”).    -   The mobility solutions should work independently of the        “transmission modes”.

3.5.2 Beam Based Active Mode Mobility

Multi-antenna transmission already plays an important role for currentgenerations of mobile communication and takes on further importance inNX to provide high data rate coverage. The challenges facing active modemobility in NX are related to supporting the high-gain beam forming.When the link beams are relatively narrow, the mobility beams should betracking UEs with high accuracy to maintain good user experience andavoid link failure.

The DL mobility concept of NX is beam-based. In deployments with largeantenna arrays and many possible candidate beam configurations, allbeams cannot transmit reference and measurement signals in an always-on,static manner. Instead, the connected ANs select a relevant set ofmobility beams to transmit when required. Each mobility beam carries aunique Mobility Reference signal (MRS). The UE is then instructed tomeasure on each MRS and report to the system. From a UE point of view,this procedure is independent of on how many ANs are involved. As aconsequence, the UE does not have to care about which AN is transmittingwhich beams; sometimes this is referred to as the UE being node-agnosticand the mobility being UE-centric. For mobility to work efficiently, theinvolved ANs need to maintain beam neighbor lists, exchange beaminformation, and coordinate MRS usage.

Tracking a moving UE is achieved by the UE measuring and reportingrelevant candidate beams' quality, whereby the system can select beamsfor data transmission based on the measurements and proprietarycriteria. The term beam switching is, in this context, used to describethe event when the ANs update the parameters, e.g., transmission pointand direction of the beam. Thus, both intra- and inter-AN beamhand-overs can be seen as a beam switches. As a consequence, hand-overin NX is executed between beams rather than cells as in traditionalcellular systems.

The beam type discussed in this section is mainly the mobility beam,which is the entity to update during mobility. Besides the mobilitybeam, there is also a ‘geo-fence’ beam which is introduced to easeinter-node mobility in some deployments.

The following two sections describes downlink mobility: choosing whichbeam/node to use for downlink transmission. One section describesdownlink measurement-based mobility and one section describes uplinkmeasurement-based. So far, it is assumed that the same beam/node is usedfor uplink communication. However, in some cases, it can be advantageousto use different beams/nodes for downlink and uplink communication. Thisis called uplink/downlink decoupling. In that case, a separate proceduremay be used to select the best uplink beam/node. Uplink measurements areused to select the uplink beam/node, and the procedures described in3.5.4 are used with minimum changes.

3.5.3 Downlink Measurement Based Downlink Mobility

Several detailed studies of mobility solution options have been carriedout, and all these formulations follow a common mobility framework,which can be summarized at a high level as in FIG. 106, whichillustrates a generic active mode mobility (downlink measurement based)procedure. After it is decided to trigger a beam switch, a set ofcandidate beams are selected for activation and measurement. These beamsmay originate both in the serving AN and in potential target ANs.Measurements are based on Mobility Reference Signal (MRS) transmissionsin mobility beams. The network decides the target beam after UE reportsthe result of the measurements to the network and optionally informs theUE of the selected target beam. (Alternatively, the UE may have beenproactively configured to autonomously select the candidate beam withthe best measurement result, and subsequently transmit the measurementreport to the target beam.) The procedure includes one or more of: UEside:

-   -   1) Measurement configuration. UE receives the mobility        configuration from network about which MRSs to measure (or the        UE could also do a full blind search without a configured list),        when to measure, how to measure, and how to report. The        measurement configuration can be performed earlier (and        continuously updated.)    -   2) Measurement. UE performs mobility measurements after UE        receives measurement activation which is instructed to start        measuring on some or all of the entries in the measurement        configuration.    -   3) Measurement report. UE sends mobility measurement reports to        the network    -   4) Mobility execution.        -   UE may receive a request to transmit USS in the UL for TA            measurement and send the USS. The requirement to send USS            can be part of measurement configuration.        -   UE may receive a command (reconfiguration) to perform beam            switch, which may include a new beam ID and a TA adjust            command. The switch command can also be first informed, and            TA can be measured and adjusted in target node.        -   Or, if the DL sync and UL TA remain valid, and the            additional configuration (new DMRS, security, etc.) is not            required or can be informed via target node, the UE may not            receive a switch command.

Network Side:

-   -   1) Measurement configuration. Network sends mobility measurement        configuration to UE.    -   2) Mobility trigger. Network determines whether to trigger beam        switching procedure.    -   3) Mobility measurement. Network decides to execute mobility        measurement procedure which includes:        -   Neighbor selection: Network selects candidate beams.        -   Measurement configuration. Network sends measurement            configuration to UE if it is not configured in step 1.        -   Measurement activation. Network activates MRS in relevant            beams and sends a measurement activation command to UE.        -   Measurement report. Network receives measurement report from            UE.    -   4) Mobility execution.        -   Network may send a USS request command (reconfiguration) to            UE to transmit USS for TA measurement.        -   The target node may measure the TA value and send the value            to the node communicating with the UE who will send TA            configuration to the UE.        -   Network may send beam switching (reconfiguration) command to            UE.

Network can send measurement configuration to UE either beforetriggering beam switching procedure (step 1) or after (during step 3).

The outlined sequence is configurable with suitable settings to serve asa common framework for all active mode mobility-related operations:first-time beam finding, triggered beam mobility update in datatransmission and monitoring modes, and continuous mobility beamtracking.

A configuration of the generic downlink active mode mobility procedurewhere the UE moves from Serving Access Node 1 (SAN1) to SAN2, as shownin FIG. 106, is described in the following section

3.5.3.1 Mobility Measurements 3.5.3.1.1 Measurement Configuration

The network may send a mobility measurement configuration to the UE.This configuration is transmitted in an RRC message and may containinformation related to measurement events—“what” (e.g., which MRSindices) to measure, “when” and “how” to measure (e.g., start time orcriterion and filtering duration), or “when” and “how” to send ameasurement report (e.g., report time slot, report best beam IDs or alsotheir powers, etc.). The list may be useful if only a small number ofMRS are turned on and can be measured on. But sending the list can beoptional for the NW and UE can perform measurements blindly, e.g.,detecting all audible MRS signals. Another example of configurabilitycould be inter-node measurements where longer filtering may be requiredto avoid ping-pong effects. For intra-node beam measurements, a shortfilter is used.

A measurement configuration may be sent by the network at any time.Typically, once the UE receives the configuration, it starts performingmeasurements. However, this procedure could be further enhanced bytransmitting an activation command in the DCI field. Thus, the RRCmessage would only configure the measurement but may not necessaryinitiate the UE to start performing such measurements.

3.5.3.1.2 Measurement Report

The UE sends measurement reports based on the configuration provided bythe network. Measurement reports are typically RRC messages sent to thenetwork. However, in certain cases, some type of reports could be sentover MAC. For the L3 based report, different number of beams can bereported concurrently, allowing to find the preferred beam in a shorttime, however it requires more signaling overhead, and it is not easy tointegrate beam switching with the scheduler. For L2 based reporting,there is less overhead, and it is easy to integrate with scheduler,however, a fixed maximum number of beam measurements can be concurrentlyreported.

3.5.3.2 Mobility Monitoring and Triggering/Execution

The MRS transmission and measurements are triggered based on theobserved link beam/node quality when data transmission is ongoing,mobility beam quality in the absence of data, or reports sent by the UE.Other triggers such as load balancing may also trigger mobilitymeasurement execution.

There are different trigger metrics and different conditions. The metricto reflect beam quality is either RSRP or SINR. The condition can be oneor more of:

-   -   a1) comparison to one absolute value    -   a2) comparison to multiple different relative values to a        reference table according to position    -   a3) comparison to values of other beams, or    -   a4) degradation rate of the link beam quality. Practical trigger        mechanisms that react to changes in the current quality metric        have also been demonstrated.

The observed beam can be one or more of the:

-   -   b1) current serving link beam (DMRS or CSI-RS),    -   b2) current serving link beam plus its ‘sector’ beam,    -   b3) current serving mobility beam (MRS).

The different types of switching (e.g., intra-node or inter-node) mayhave different thresholds. For example, when link quality is worse thanthreshold 1, intra-node beam switch is triggered. When link quality isworse than threshold 2, inter-node beam evaluation and switching istriggered. If excellent backhaul (e.g., dedicated fiber) is present andthere is no problem with ping-pong effects, both intra-node andinter-node can use the same parameters.

When the network decides that a serving beam/node identity need to bechanged/updated/modified, the network prepares the mobility procedure.This may imply some communication with other nodes in the network.

There are several options for reporting the MRS measurement results tothe network:

-   -   c1) If the UE reports all measurements to the serving node, the        serving node determines the node to switch to and signals to the        UE. This approach relies on the existing serving link for all        signaling during the mobility procedure. TA towards the new        serving beam is estimated in conjunction with the switch        command. Details of TA estimation are covered in section        3.5.3.4.    -   c2) If the UE reports the measurements back to the individual        nodes where the different MRS came from, the reporting itself        requires a previous USS transmission and TA estimation—it is        then seen as part of the measurement procedure. Once the NW has        decided the new serving node and signaled to the UE, the UE uses        the already available TA towards the new serving node. This        approach requires more UL signaling, but removes the critical        dependence on the old serving link once the measurement command        has been issued.    -   c3) Similar to c2), but the UE reports all the measurements back        via the serving beam and via the best of the measured new beams.        Then, only one TA estimation procedure should be conducted.

Eventually, the network may request the UE to apply a new configuration.There may be situations in which a reconfiguration could be transparentfor the UE, e.g., in an intra-node beam switch. The reconfiguration thenhappens on the network side, a serving beam/node may be changed;however, the UE keeps the existing configuration. If a reconfigurationis needed, it can be configured before or after the switch.

3.5.3.3 Infra/Inter Node MRS Activation/Deactivation

In general, the MRS is only transmitted based on demand. The networkdecides which candidate beams, or neighbor beams, should be activated.Candidate beam selection can be based on, e.g., a beam relations lookuptable. This neighborhood lookup table is indexed by either UE positionor radio fingerprint. The position can be the accurate position (GPSinfo) or an approximate position (current serving beam info). Creatingand maintaining the neighborhood lookup tables is a generalization ofthe automatic neighbor relations (ANR) management process, handled bythe SON functionality in the network (cf. section 3.9.4). The tables canbe used both for providing trigger criteria (section 3.5.3.2) toinitiate a measurement session towards a given UE and for determiningthe relevant candidate beams for measurements and a possible beamswitch. The beam in this lookup table can be either a normal mobilitybeam or a ‘sector’ beam. The neighbor beam relationship table size canbe reduced; both from the memory consumption and from the signalingconsumption perspective, if the candidate beams are wide and the numberof beams is lower. In some network deployments, e.g., deploying NX inLTE frequency bands or in a high load and frequent handover area, it maybe preferable to configure the MRS to be always-on, so that potentiallymany UEs that are covered by the same mobility beams can continuouslytrack the quality of neighbour beams.

3.5.3.4 Timing Advance Update

To report MRS measurements to nodes other than the serving node, and toresume UL data transmission towards a new serving node, the UE needs toapply correct timing advance, which typically differs from the TA forthe current serving node. In a non-synched NW, the TA estimation alwaysneeds to be performed. USS transmission is then configuredper-measurement in the MRS measurement command or statically by RRC. Thesame applies in synched macro NWs, where the ISD exceeds or iscomparable to the CP length.

In a tightly synched NW with short ISDs, on the other hand, the TAtowards the old serving node may also work well for a new serving node.The UE can deduce whether that is the case from whether the old DLtiming sync works for the new node. It would be efficient not to do newTA estimation unless really necessary. The NW-controlled approach isthat the NW configures the UE to transmit the USS (or not) on aper-measurement basis in the MRS measurement command. TA is notestimated if the NW estimates that the old and new nodes can share thesame TA value, otherwise the UE is requested to send USS. Alternatively,in a UE-controlled approach, the UE can omit sending USS in the UL if itdetermines that no re-sync was necessary to measure the new node's MRS.Here, the node still needs to reserve resources for USS reception.

If the TA is to be changed, this is conveyed using dPDCH or PCCH eitherover the old serving beam or from the new node (where the DL is already“operational” since the UE has synched to the MRS).

In MRS reporting solution c1 above, the USS may be sent in the UL and TAupdate in the DL may be sent as part of the beam switch command andhandshake.

In MRS reporting solutions c2 and c3 above, the UE sends the USS as partof the measurement report procedure towards an MRS-transmitting node,and receives a TA update as a separate message.

In some deployments, where the UE position may be determined with highaccuracy, the required TA correction when switching from old servingbeam to a new one may be retrieved from a previously collected database.The database is created based on previous TA measurements managedaccording to SON principles.

3.5.3.5 Configurable Sequences

The mobility measurement sequences are essentially the same as in LTE.The mobility monitoring and triggering sequences are similar to those inLTE, but some details differ, e.g., the criteria of launching and theUE-specific signals available for mobility measurements. The MRSactivation sequence where reference signals (MRS) are activateddynamically in a UE-specific candidate beam set is a new procedure inNX. Activating and deactivating MRS on request, and in a UE specificmanner is critical for lean design. The main new challenge in NX is forthe network to decide which candidate MRSs are activated, and when. Thelatter aspect may be especially critical at high frequencies due toshadow fading. Some preparations and signaling may be needed in thenetwork when candidate beams are activated in several different nodes.Nevertheless, this procedure is transparent to the UE. The UE is onlyinformed about the measurement configuration and the UE reportsaccordingly, without having associated the beams with specific nodes.The TA update sequences can also be measured and adjusted in target nodeafter the switch command is first informed. Also the additionalreconfiguration is probably required.

The beam switch triggering procedure differs depending on how MRS isdesigned and transmitted. More specifically there are three typicalcases:

-   -   1. The beam MRS is only activated when serving beam quality        degradation is detected. MRS for all relevant candidate beams in        the lookup table are activated, no matter if the beam is from        the same node or from a neighboring node. The table building can        be part of the SON functions. The UE measures on all the MRSs        and sends the measurement report.    -   2. Either all the sector MRSs in the lookup table or the sector        MRS containing the serving beam for the active UE is configured        and transmitted periodically. UE can also keep track of the        quality of the transmitted sector MRS and report the quality        periodically or in an event-based manner.    -   3. The serving mobility beam is adapted to continuously track        the UE to maintain the maximum beam gain, which is similar to        the CSI-RS procedures in section 3.4. The UE reports an error        signal between the current serving beam direction and the        estimated best beam direction, using additional beams in the        neighborhood of the serving beam.

Case 1 is more suitable for services without strict QoS requirements,while case 2 is more suitable for time critical service with additionaloverhead. (There are also hybrid options, e.g., activating all the MRSsin the lookup table for a given UE, with additional overhead.) In case3, with UE specific reference symbols, any modification of beam shapewithin one node can be transparent to the UE—no signalling is required,unless RX analog beamforming is applied in the UE side.

3.5.4 Uplink Measurement-Based Downlink Mobility

It is also possible to use uplink measurements to select downlink beam.On a high level, it can be assumed that such measurements are performedon demand, when a beam switch is deemed necessary. Hence, the concept ofa mobility event still applies, and some sort of trigger to start theevent is relied upon.

Since the downlink beam is being updated, it is natural to still monitorthe downlink performance, using any of the measurements described in theprevious section. For instance, CQI measured on CSI-RS or MRS may bemonitored.

Using uplink measurements to choose the AN used for downlinktransmission usually works well, providing that different ANs use thesame transmit power and have the same antenna capabilities. Otherwise,this has to be compensated for.

To use uplink measurements to select downlink beam within one node,reciprocity between uplink and downlink is desirable. Passive antennacomponents and the propagation medium are physically reciprocal for TXand RX, but active components and RF filters in the RX and TX pathstypically exhibit asymmetries and phase variations that do not yieldautomatic reciprocity in all cases. However, by introducing additionalHW design constraints and calibration procedures, any desirable degreeof reciprocity may be provided.

As discussed in detail in section 3.4, different levels of reciprocitymay be distinguished:

-   -   “Directional”: Angles of arrivals/departures are reciprocal for        RX and TX,    -   “Stationary”: Channel covariance matrix is the same for RX and        TX    -   “Coherent”: RX and TX channels match, as seen from baseband        within coherence time/bandwidth

For the purposes of mobility, generally aiming at a proper grid-of-beamsbeam selection across many fading cycles, directional reciprocitytypically suffices. Pairwise antenna element calibration techniques inthe TX and RX paths can provide the required inter-element phasecoherence. “Directional” reciprocity allows using UL measurements fordownlink TX mobility beam switching as well in the discussedgrid-of-beams configurations.

To obtain the uplink measurement, the network requests the UE to send ULreference signals to the network. One possible reference signal formobility measurements is the USS. The USS can be detected not only bythe serving node, but also by the neighbor nodes. The neighbor nodesshould hold transmissions of UEs that they are serving, to clear thetransmission resources where the USS will occur.

If the coverage situation is challenging, the UEs may need to use TXbeamforming to transmit the USS. In this case, the UE is required totransmit the USS in all candidate directions, and different USSidentities may be allocated to different uplink TX beams in the UE sideso that the network can feed back the best UE TX beam identities. If theUE cannot transmit in more than one direction simultaneously, the beamstransmissions may be time-multiplexed. The USS can be transmitted fromthe UE periodically or be event triggered (when the quality of the linkbeams degrades). Such beam sweep configuration is more complicated inthe UL than in the DL, due to the irregular UE antenna array layout.Suitable sweep patterns may be determined in several ways using priorcalibration or on-the-fly learning by the UE.

In the network, the candidate AN attempts to detect the USS in differentbeams, and selects the best beam. If analog beam forming is used by thenetwork, the nodes cannot perform the measurement of a large number ofbeams in one USS period. The AN can scan the USS using different RXbeams sequentially. Coordination of UE TX and AN RX beam sweep patternsis complicated. Relying on this combination should only be considered ifreally mandated by the coverage requirements.

There are some requirements on signaling between UE and network, whichinclude, e.g., the number of USS used in UE and the repetition periodfor network scanning. It may be assumed that the same procedure isadopted as for MRS configuration: configure USS transmission parametersusing RRC, and activate transmission using MAC.

There are several alternatives to perform downlink beam switching basedon the uplink measurement.

-   -   1. The narrow (link) beam can be selected directly based on the        uplink measurement.    -   2. The beam selection based on the uplink measurement decides        the mobility beam, and the narrow (link) beam can be selected        based on the complemented downlink measurement later.    -   3. The mobility beam is first decided by the uplink measurement        with a wider RX beam. After that, the narrow (link) beam can be        further decided by uplink measurements with narrow RX beam. When        deciding the narrow beam, the other RS might be measured in the        narrow beams that are located within, or in the vicinity of, the        selected RX beams in first part.

In the three alternatives, the beam selection procedures (beam selectionin alt. 1, wide beam selection in alt. 2 and alt. 3) are similar,illustrated in FIG. 107. The procedure of the beam selection based onthe uplink measurement can briefly be expressed as follows:

-   -   1 Trigger beam switch    -   2 Activate USS reception between neighbor nodes in relevant        beams    -   3 Activate USS transmission in UE    -   4 Perform USS measurement in network    -   5 Determine the best beam based on the measurement report    -   6 Prepare beam switch if needed    -   7 Issue beam switch command if needed

As said previously, the USS can be transmitted from the UE periodically,or in an event-triggered manner. If the USS is transmitted periodicallyaccording to the early configuration, steps 1-3 can be ignored. If atiming advance update is needed, the TA value can be obtained from theUSS measurement and the new TA value can be informed to UE during beamswitch command. Details of TA estimation are similar to the descriptionin section 3.5.3.4. In the narrow (link) beam selection of Alt3, thereis only one small difference, where the beams from neighbor node are notinvolved. It is a kind of intra-node beam selection, which isillustrated in FIG. 108. Here the “USS” could also be other type ofreference, such as RRS. The complemented downlink measurement in Alt 2is similar as the intra-Node beam switch in case 2 of downlinkmeasurement based method.

3.5.5 Radio-Link Problem

Given a system that is “ultra-lean” and uses massive beam-forming, thetraditional definition of a “radio link failure” needs to bere-considered. When data is not transmitted in either uplink or downlinkthere might not be any signal that can be used to detect that the radiolink is failing. Mobility reference signals may, for example, not alwaysbe present in an ultra-lean 5G system.

A user terminal may move out of coverage between packet transmissionbursts without being noticed. If in-band and/or beam-formedcontrol-information is relied upon, it may not always be possible toreach the intended receiver to continue data transmission to this UE.Alternatively, when a user wants to send data it may not be able tocommunicate this to the network and be scheduled. In such a scenario theUE has to perform a new random access procedure, which is associatedwith a significant delay and signaling overhead cost.

For this purpose, a new event denoted a radio link problem (RLP) isintroduced. This is used to indicate that there is a mismatch betweenthe network node and user terminal node configuration of the radio link.An RLP can be caused by a network node antenna pointing in a directionwhere the signal does not reach the intended UE. It may also be causedby an antenna configuration in the user terminal that is not tuned inproperly towards the intended serving node in the network.

Note that this section considers only the case where there is asituation that is different from a traditional radio link failure (RLF)in the sense that a radio link problem (RLP) is not an “error event” butsomething that happens rather frequently. Instead of maintaining a radiolink, it can be “fixed,” when needed. An RLF type of event may also beused for NX, where the UE really attempts to re-establish using the“normal” access procedure. This may, for example, be triggered if RLPrecovery fails. This is not considered in this sub-section.

A fast radio link problem (RLP) resolution procedure is designed tore-establish a radio link between a UE and the network if needed. The UEmay detect an RLP event as one or more of:

-   -   Expected DL signal “disappears” (e.g., scheduled or periodic        DL-reference signal falls below a threshold). A timer may be        configured for how long the signal needs to be below the        threshold before RLP is detected.    -   A monitored DL signal “appears” (e.g., scheduled or periodic        DL-reference signal is above a threshold). A timer may be        configured for how long the signal needs to be above the        threshold before RLP is detected.    -   No response on UL transmission (typically after a scheduling        request transmission or a contention-based channel        transmission). A counter may be applied for how many        transmissions need to be un-responded before detecting RLP.

In addition, the NW node detects an RLP event as one or more of:

-   -   Expected UL signal “disappears” (e.g., scheduled or periodic        UL-reference signal falls below a threshold). A timer may be        configured for how long the signal needs to be below the        threshold before RLP is detected.    -   A monitored UL signal “appears” (e.g., scheduled or periodic        UL-reference signal is above a threshold). A timer may be        configured for how long the signal needs to be above the        threshold before RLP is detected.    -   No response on DL transmission (typically UL grant or DL        assignment). A counter may be applied for how many transmissions        need to be un-responded before detecting RLP.

In case the normal (high bit-rate) data traffic occurs in a high antennagain narrow beam, there may be a pre-configured fallback proceduredefined that used another more robust beam (typically lower data rate,lower antenna gain, wider beam-width).

In FIG. 109, which illustrates an example in which the UE detects aradio link problem and the serving node resolves the problem, the UE isthe node that detects an RLP in the first (e.g., narrow beam) radiolink. Note the narrow oval shapes that schematically depict the networkside and the UE side antenna configuration for this first radio link.After detecting the RLP event, the UE sends an UL RLP transmission,possibly using a new antenna and more robust configuration(schematically depicted by the right-hand circle in FIG. 109). Theserving network node starts, possibly after an inactivity timer hasexpired, an uplink monitoring for UL RLP transmissions from the servedUE. This reception may be performed using a more robust (e.g., wider)beam (schematically depicted by the left-hand circle in FIG. 109). TheUE may identify itself in the UL RLP transmission by using a pre-definedpublic identifier, here denoted tag_(p), while the serving node mayidentify itself in the UL RLP repair response transmission using theidentifiers, or tags tag_(p) (public) and tag_(s) (serving). When theserving node has several radio links active it knows by examining thereceived identifier (tag_(p)) which radio link that has a problem. Whenthe UE is prepared to receive an UL RLP repair response from anon-serving node it then has the possibility to distinguish anon-serving node response (that uses the public identifier tag_(p)) froma serving node response (that uses a serving node identifier tag_(s)).Once both nodes, the serving node and the UE, are both aware of the RLPevent, then the natural next step is to perform a new optimizationprocedure for the radio link. Alternatively, the radio link can beallowed to remain “broken” until it needs to be fixed for the purpose oftransmitting user data again. In that case the next transmission shouldpreferably start with a robust antenna configuration on both sides. Asimilar procedure is used in case the RLP is first detected in the NWnode.

3.6 Self-Backhaul

One of the features of NX is the integration of access and backhaulusing the same basic technology and possibly operating over a commonspectrum pool, including operation over the same physical channel orwithin different channels in the same band. (The use of out-of banddimensioning of access and backhaul is not precluded.) As a desiredresult of such integration, a base station or an access node (AN) shouldbe able to use the NX technology for both wireless access and wirelesstransport over, possibly, the same spectrum. This capability is hereinreferred to as self-backhauling, and self-backhauling in NX maytherefore use the access components (e.g., multi-access,synchronization, multi-antennas, spectrum, etc.) supported in NX but forbackhauling purposes.

3.6.1 Motivations and Scope

“Small-cell” access nodes can only cope with the anticipated growth inwireless data traffic in cooperation with a robust and capable transportnetwork. There are situations in which no fixed backhaul connection suchas optical fiber is available at locations exactly where additional basestations are needed. Dedicated carrier-grade wireless backhaultechnology is a cost-effective alternative to fiber and is usuallyassociated with high spectral efficiency, high availability, lowlatency, extremely low bit error rates, and low deployment cost. The useof wireless backhaul does not only put requirements on the technologyitself but also requirements on interference handling which is usuallydone via careful planning and licensing. The traditional wirelessbackhaul deployment is typically a single LOS hop.

The continuous evolution of radio access drives the backhauldevelopment, e.g., need for higher and higher capacities, densification,etc. Future wireless backhaul deployments will also in many cases facethe same challenges as faced by radio access, e.g., NLOS channels withsignal diffraction, reflection, shadowing, multipath propagation,outdoor-to-indoor penetration, interference, multiple access, etc.Wireless backhaul of moving base stations, e.g., those placed onhigh-speed trains, is an important use case. The performancerequirements on backhaul are much higher than those placed on the accesslink, but the deployment scenarios are likely engineered carefully,often towards stationary scenarios. The high performance requirementsmay be met by the same techniques used for access networks, namely MIMO,multiple access, interference rejection, mobility etc. This forms thebasis of access and backhaul convergence as well as self-backhauling.

The NX design supports both in-band (where access and transport use thesame spectrum) and out-of-band (where separate spectra or carriers areused for access and transport) self-backhauling. In-band self-backhaulrequires only a single block of radio spectrum for both access andtransport and is attractive when acquiring a separate spectrum fortransport over the entire coverage area is costly or difficult. In-bandself-backhaul also simplifies the hardware, and reduces the associatedcost, with a common set of radio transceiver and antenna system.However, when the intended coverage areas of access and transport aresubstantially different, out-of-band backhaul with separate spectra anddedicated hardware may be desirable. Moreover, in-band self-backhaul cancause mutual interference between access and backhaul links and is thusmore challenging than its out-of-band counterpart. To mitigate theimpact of mutual interference, radio resource may be shared betweenaccess and transport through a fixed allocation in time or frequencydomain. Alternatively, the resource sharing may be accomplished in adynamic manner according to the traffic demands through jointradio-resource management between access and transport to maximizespectral efficiency.

In order to support a variety of different target use cases described inthe next subsection, the NX design also supports self-backhauling overmultiple (two or more) hops, where the number of hops is counted onlyover backhaul links, excluding the access link. The multi-hop aspectposes challenges in protocol design, end-to-end reliability assurance,as well as radio resource management.

3.6.2 Target Use Cases

The target use cases for self-backhauling may be classified into threegroups roughly differentiated on the basis of two main characteristics:topology and availability. The groups may be listed as:

-   -   I. Static or Deterministic topology, high availability,    -   II. Semi-static topology, medium availability, and    -   III. Dynamic topology, low availability,        where the availability varies as five nines (i.e., 99.999%), 3-4        nines, and 0-1 nine(s), respectively. Among all these use cases,        some have been prioritized for attention, because they are        either representative or exemplary use cases. FIG. 110        illustrates the prioritization of the use cases as the sequence        II.4.b, II.2.b, II.3.a, I.1.a, II.2.c, III.6, III.7, I.1.b,        II.2.a, II.3.b, II.4.a, II.4.c, III.5.

The topology of a self-backhaul network is generally a mesh, but it isexpected that simpler routing constructs would be superimposed on theconnectivity graph. There is usually a tendency to minimize the numberof hops needed to traverse the local network; in most cases this leadsto the maximum number of backhaul hops to be limited to 2-3 hops. Thereare however exceptions, such as the high speed train, where the numberof hops may grow to a much higher number, such as the number ofcarriages in the train. (It is certainly true that train carriages canbe connected with wired technology, but this brings the additionalcomplication of having to bridge the initial backhaul access towards awired LAN with adequate transport capacity.)

The transport format on the backhaul should be flexible. Thus, while itis advantageous that the basic air interface used for NX multiple accessand NX self-backhaul links be identical, the air interface should becapable of supporting a wide span of availability requirements rangingfrom 99.999% or five nines for traditional backhaul replacement to 0-1nine(s) of availability for the V2V use case. (Many use cases for ITSare not subject to high reliability or low latency requirements, andthere are limitations for provisioning high availability for largenumbers of vehicles simultaneously.) Important use cases are describedin detail below. FIG. 111 illustrates some cases of importance forself-backhaul with a diversity of performance requirements in terms ofavailability, latency and data rate requirements.

TABLE 15 A tabulation of important KPIs for self-backhaul RequirementsSmall Long- Cell Public haul KPI Backhaul Event Train Safety transportLink 500 5 km 1 100 1 500 200 m 20 5 distance m km m km m km km Fre- 306 6 30 6 30 >700 6 30 quency GHz GHz GHz GHz GHz GHz MHz GHz GHz BandHops 1-2 1-3 1-10 1-2 1-2 (back- haul) Band- 500 MHz 200-500 200-500 —200-500 width MHz MHz MHz Avail- 99.9- 95% 99.9% 99.9% 99.999% ability99.99% Radio 50-100 us 250 us 250 us — 250 us Latency Total 1-2 ms 1-2ms 10 ms — 500 us Latency (one way E2E) Data 1-10 GB/s 200 Mb/s 0.8 2 102-10 Gb/s Rate (user) Gb/s Gb/s Gb/s

3.6.3 Working Assumptions

To define the scope and set the focus of the NX self-backhaul concept,the following assumptions are made:

-   -   1. Self-backhauling (BH) access nodes (ANs) are intended to work        in a time synchronized manner.    -   2. Multiple hops (unlimited) are supported, but performance is        optimized for 2-3 hops at most.    -   3. In-band and co-channel use of access and backhaul are        supported (access and backhaul do not necessarily share the same        spectrum, but are allowed to do so).    -   4. Homogeneous backhaul links that only use NX interface.    -   5. Access interface is not necessarily NX (e.g., maybe LTE or        WiFi).    -   6. Routes are assumed to be fixed over significant time periods        and may be switched at Layer-2 in local environments or at        Layer-3 in the wide area.    -   7. The self-backhaul links support all necessary network        interfaces, such as S1/X2 and BB-Cl/BB-CU, so that core network        functionality can be maintained across backhaul links when used        for transport. For distributed eNB implementation where higher        layers may be conducted in cloud hardware, the support of other        interfaces may also be needed.

3.6.4 Unified View of Access and Backhaul

To achieve a harmonized integration of access and backhaul, a unifiedview of the access links (between UE and AN) and the backhaul links(between neighboring ANs) is highly desirable. As illustrated in FIG.112, a self-backhauling base station or AN serves not only its ownassigned UEs, referred to here as the normal UEs or just UEs, in itsvicinity as a base station but also its neighboring access nodes as arelay to route data towards and from the core network. Eachself-backhauling AN can be considered as a combination of a virtual ANand a virtual UE positioned at exactly the same physical location. Anaggregation node (AgN) serves as a special, root node in such a networkof ANs that has a fixed (wired) backhaul connection, where all datatraffic originates from and terminates at. With this viewpoint, eachbackhaul link can be treated as an access link between a virtual UE of adownstream AN and a virtual AN of an upstream AN. The entire multi-hopnetwork can thus be seen as a traditional cellular network with onlysingle-hop access links between (virtual or normal) ANs and UEs. Bothbackhaul links and access links can be treated in the same manner, andany control channels and reference signals defined for access links canbe re-used in backhaul links. However, as discussed later in thesubsection on route selection, the NX design needs functionality thatestablishes a routing table at each self-backhauling AN. This may forexample be achieved by means of a protocol layer such as the RLC or byan adaptation component of layer 3 such as the PDCP.

FIG. 112 illustrates a device co-location perspective ofself-backhauling access nodes.

3.6.5 Multi-Antenna for Backhauling

High capacity and spectral efficiency are important for backhaul in muchthe same way as access. Multi-antenna technologies like MIMO and spacediversity that traditionally have been adopted in radio access have alsobeen adopted to increase spectral efficiency and reliability indedicated wireless backhaul systems. Antenna diversity is commerciallyavailable and LOS MIMO is becoming commercial in microwavepoint-to-point backhaul (MINI-LINK). Future and more flexibledeployments in heterogeneous networks are also making beamforming orbeam steering interesting desirable features in wireless backhaul.Beamforming has the twofold advantage of improving received signalpower, while reducing the amount of interference to other users byconfining transmissions towards desirable directions.

The multi-antenna concepts developed for NX, for the above reasons,provide increased coverage, reliability, spectral efficiency, andcapacity for self-backhauling use cases.

In contrast to an access link, a typical self-backhaul use case has anaccess node at each end of a link which makes it possible to have moreadvanced antenna systems in both ends. This opens up for possibilitiesto use higher order SU-MIMO to increase spectral efficiency and/orreliability. In some use cases, e.g., small-cell backhaul, MU-MIMO canadvantageously be used. In an in-band self-backhauling implementation,MU-MIMO can also be applied to multiplex backhaul and access trafficover the same resources. MU-MIMO combined with multi-layer transmissionto each self-backhauled access node may also have potential.

The performance of multi-antenna schemes depends on the quality of theCSI that is used to design the transmission/reception. If the radio basestations are fixed and the channel has longer coherence time, then thereis also better possibility to acquire high-quality CSI to design morerobust high-capacity multi-antenna transmission/reception schemes. Pilotcontamination in reciprocity-based massive MIMO also becomes less of aproblem if the channel does not have to be re-trained that often.Reciprocity-based multi-antenna techniques in NX rely on up-linkmeasurements to design down-link transmissions to reduce or eliminatethe need for CSI feedback. However, if the channel is more or lessstatic which it might be in some backhaul scenarios then it can bepossible to also consider FDD since associated overhead due to CSIfeedback becomes smaller if the channel does not have to be trained thatoften thanks to longer coherence times. Reciprocity is easier to exploitwith unpaired spectrum, but may also be achieved using statisticaltechniques for paired spectrum. (For example, covariance estimation canbe used to determine dominant eigenmodes for the channel that arereasonably long-lived; these techniques can improve receiver SNR metricswithout needing instantaneous channel information.) Additionally, itbecomes much easier to set up a link and to identify the good beams in abeam-based system when the channel has a long coherence time and thelocations of the nodes might even be known. Static backhaulingapplications have clear advantages which makes it possible to claim thefull potential of multi-antenna systems.

Self-backhauling in NX should support both in-band and out-of-bandoperation which may put requirements on the antenna system used forbackhaul. For example, if there is a large carrier frequency differencebetween access and backhaul links in an out-of-band solution then thereis an obvious need to use separate antenna systems for access andbackhaul that are adapted to their respective frequency. The sameantenna system can in an in-band solution be used for both access andbackhaul links. However, using the same antenna system has implicationson the backhaul coverage area since all backhaul links need to be withinthe same coverage area as the access links which might not always be thecase. If different coverage areas are desired for backhaul and access,then separate antenna systems should be considered also for the in-bandcase. Depending on the backhaul requirements, a separate antenna systemmay also be desirable to achieve a good enough link budget for thebackhaul connection.

3.6.6 Protocol Architecture

An important issue is the protocol architecture for self-backhaul. Frompurely protocol architecture point of view, there are three mainalternative approaches:

-   -   L2 relay    -   L2 relay (as per LTE relay)    -   L3 relay (as per WHALE concept)

The present design focuses on the architecture described in FIG. 113 andFIG. 114 (L2 relay).

3.6.6.1 L2 Relay

FIG. 113 and FIG. 114 show, respectively, the protocol architectures ofuser plane and control plane for multi-hop self-backhaul, where eachself-backhauling AN is treated as a L2 relay. In this architecture, eachself-backhauling AN essentially serves as a L2 proxy of the downstream(virtual or normal) UE towards its upstream AN.

The L2 relay approach can be combined with multi-hop ARQ, as discussedmore in detail in Sections 2.2.8.4 and 2.2.8.5.

3.6.6.2 L2 Relay (as Per LTE Relay)

Alternatively, FIG. 115 and FIG. 116 show the protocol architecturesadopted by LTE relay concept, for one-hop relaying, for user plane andcontrol plane, respectively. With this architecture, a self-backhaulingAN corresponds to an LTE relay, and an aggregation node corresponds to aLTE donor eNB. With this architecture, a self-backhauling AN can beviewed as essentially serving as a proxy of the upstream AN towards itsdownstream (virtual or normal) UE. As a result, the backhaul links needto carry S1/X2/OAM signals with associated tight requirement onavailability and latency. It is unclear whether this architecture can beextended to the cases with multiple (two or more) hops, and, if so, whatthe benefits of this architecture are compared to that described in FIG.113 and FIG. 114.

3.6.6.3 L3 Relay

A third approach is to implement a separate underlying transport networkusing wireless technology (such as NX). This architecture can bedescribed as one wireless application stratum on top of an underlyingwireless backhaul stratum. In FIG. 117, a high level architecture forthis alternative is illustrated. Even if the figure only illustrates asingle hop in the backhaul stratum, this can be extended to multiplehops, by including L2 relay as part of the backhaul stratum, e.g., asdescribed above in Sections 3.6.6.1 or 3.6.6.2.

As the application stratum interfaces wireless backhaul on the IP layer,this alternative can also be described as “L3 relay”, note that the userplane core network nodes used by the application stratum are typicallythe same as those for the backhaul stratum, e.g., using piggybacking ofthe core network user plane nodes.

An important characteristic of this alternative is that the wirelessbackhaul is access-agnostic—the underlying wireless is a generictransport network that can be shared by several wireless networkapplications (different types of access nodes).

3.6.7 Route Selection

In order to transport information wirelessly from an aggregation node,which is assumed to have a wired connection to the core network, to a(normal) UE, or vice versa, through a network of self-backhaul ANs, eachself-backhauling AN has to know where to forward a received NX PDU inthe next hop for each individual (normal) UE and for at least oneaggregation node. Hence, each self-backhauling AN should maintain arouting table that contains such next-hop routing information andcontext for all registered (normal) UEs. As the wireless environment canchange over time, this routing table needs to be periodically updated ateach self-backhauling AN, albeit relatively infrequently. These routingtables collectively determine a route between each (normal) UE and anaggregation node. In the following, several options for establishingthese routing tables and the associated routes are considered for NX.

3.6.7.1 Fixed, Predetermined Routing

The routing table (and the associated routes) are pre-determined duringdeployment, and do not change over time. In this case, no periodicrouting functionality needs to be implemented in the network. Eachvirtual UE of a self-backhauling AN is assumed to be attached to atleast one fixed virtual AN of another AN or aggregation node.

3.6.7.2 Implicit Routing Through Serving-Node Selection

With the unified view of access and backhaul links described in Section3.6.4, route selection may be accomplished implicitly by applying thetraditional serving-node selection mechanism on the virtual UE of eachself-backhauling AN. By restricting that the virtual AN of eachself-backhauling AN can only be activated after a connection with thecore network is established by the virtual UE of the self-backhaulingnode through other self-backhauling ANs or aggregation nodes, a treetopology of routes rooted at the core network can be established for allself-backhauling ANs. A routing table can thus be established at eachself-backhauling AN by forwarding the identities of descendant ANs tothe upstream AN on the route tree. A logical control channel should bemade available in NX, for forwarding these AN identities or otherrouting information in general.

The advantage of such implicit routing through serving-node selection isthat no explicit routing function is needed, and the mobility solutionsdeveloped for NX can be reused for routing purposes. When the channelcondition between a virtual UE and a virtual AN changes, due to thechange of the environment or the mobility of the ANs, the virtual UEshould handover to a new virtual AN corresponding to anotherself-backhauling AN, and as a result, the routes of all descendent ANsof the virtual UE will change accordingly. A drawback of the implicitrouting is that the selection of each link in the route tree is basedpurely on the local channel conditions (for handover) withoutconsidering the impact of the selection on the throughput of each route.

3.6.7.3 Explicit Routing

In order to optimize the throughput and the latency of self-backhaulconnections, route selection should ideally take into account both theinterference generated by neighboring links that constitute the route(intra-route interference) and the interference generated by links thatconstitute the other routes (inter-route interference). Suchinterference-aware routing can only be accomplished by an explicit,dynamic routing function. The explicit routing function can beimplemented in a centralized or distributed fashion.

In a centralized (explicit) routing function, all routing and resourceallocation decisions are taken by a single central node (e.g., anaggregation node) that is assumed to have access to all relevant channelstate or distribution information about all nodes and links in thenetwork. The centralized implementation allows the use of not onlyinterference-aware routing solutions, but also energy-efficientnetwork-coding-based routing solutions. Such a solution has thereforethe potential of leading to the best overall selection of routes andradio resource allocations. However, it requires a significant amount ofoverhead to periodically forward all channel information to the centralnode over certain end-to-end logical control channel.

In distributed routing, the (explicit) routing function is collectivelyimplemented by all self-backhauling ANs. Each node makes individualdecisions on where to forward a packet to reach a target node based onlocal channel measurements and local exchanges of routing informationwith its neighbors. Collectively, the set of decisions made by all nodesforms the overall selected route(s) and allocated resources in thenetwork. An advantage of distributed routing is that the routingfunction scales well with the network size. A challenge is to set upnecessary control channels to facilitate the exchange of routinginformation among neighbor ANs.

The NX design initially supports the first two more basic routingsolutions, namely, the fixed routing and the implicit routing, whilepaving the way for evolution to more sophistical explicit routingsolutions in the future.

3.6.7.4 Physical-Layer Network Coding

Unlike wired networks, routes carrying different traffic causeundesirable mutual interference in wireless networks. This fundamentallylimits the performance of routing as the routing solution was originallyintended for wired networks with isolated connections and cannot easilybe extended to cope with the interference in wireless networks.Physical-layer network coding (PLNC) schemes may be used for multi-hopcommunications in wireless networks. They have the ability to exploitthe broadcast characteristics of wireless medium, treat the interferenceas useful signals, and disseminate data over multiple routes thatnaturally arise in a wireless medium. PLNC schemes may also beintegrated with the routing paradigm by applying the PLNC schemes overroutes that are severely interfering with each other.

FIG. 118 illustrates routing vs. PLNC. The left side of the figure showsrouting of two packets on two separate routes. Each relay node receivesa mixture of the two packets and needs to reconstruct the desiredpacket. Therefore, packets create mutual interference at the relays. Theright side of the figure shows the PLNC approach: both relay nodesforward the received mixture of packets. None of the packets is viewedas interference at the relays.

There are a number of different PLNC schemes, but the most promisingones are compute-and-forward (CF) and noisy network coding, which isalso sometimes referred to as quantize-map-and forward (QMF). There aretwo important ideas behind these schemes that routing lacks. First, arelay AN does not have to decode every data packet it wishes to forward.Since decoding in a wireless channel is difficult due to the fading,noise, interference and limited received power, relaxing the decodingconstraint boosts the network performance. Instead, the relay can sendsome quantized information about the received packet. This allows anynode (even if it cannot decode) to forward data towards the destination,which in turn boosts the network robustness and flexibility. The maindifference between CF and QMF lies in the way such quantized informationis produced.

Second, a relay AN can simultaneously send information received frommany transmitters. For example, the relay that receives a combination ofmultiple packets that sum together in the air can forward thatcombination of packets. The destination node receives in due coursemultiple different combinations of packets from the relays and resolvesthe individual packets via linear algebraic methods. Such simultaneoustransmission of multiple packets leads to a more efficient bandwidthutilization. The same idea, which is also present in the traditionalnetwork coding, is illustrated in FIG. 118. In routing, packets sent viadifferent routes are mutually interfering. In the PLNC approach, theyare viewed as useful information at every relaying AN.

3.6.8 Multi-Hop Retransmission

Important use cases of self-backhaul, such as small-cell backhaul andevent-driven deployment, impose new requirements on the protocol stackthat are desirable to provide support for multi-hop communications.Different L2 protocol architectures result in different design optionsfor L2 functionalities, such as the ARQ, regarding multi-hopcommunications.

For LTE relay, the relay takes on dual roles. It appears as a regularbase station to its own UE and as a regular UE to its own base station,fully reusing the LTE radio interface with its protocols and procedures.Essentially the same radio protocols are reused on the backhaul, exceptfor certain control plane protocol additions. This is to a large extentconsistent with the unified view of access and backhaul described inSection 3.6.4. However, the LTE two-layered ARQ protocol, i.e., RLC ARQand MAC HARQ, is originally designed for single hop communication onlyand is not directly extendable to support multi-hop communication.

Basically, there are several options for designing the multi-hop ARQprotocol architecture. The simplest way is that each hop performsindependently ARQ and HARQ just like LTE single hop, which howevercannot support end-to-end reliability. Alternatively, each hop can haveindependent HARQ but for the end node (BS and UE), a RLC ARQ is added toensure end-to-end reliability. Yet another option is that a common ARQcan be introduced over multiple hops, utilizing Relay-ARQ. Here, ARQtimers and handling are improved by delegating responsibility of packetdelivery to the next hop but still maintaining the data in the bufferuntil a confirmation of delivery to the final destination is received,this can improve efficiency compared to an end-to-end ARQ since messagesonly need to be retransmitted over the link that failed. Refer toSection 2.2.8.4 for more details.

3.6.9 Self-Interference Avoidance

Despite the recent advances in full-duplex communications, a majority offuture 5G devices (base stations or UEs) is expected to be still onlycapable of half-duplex communications over any given frequency band. NXtherefore supports such devices, which are restricted not to transmitand receive data at the same time over the same frequency band in orderto avoid self-interference. As a result, at any given time over anygiven band, all the self-backhauling ANs in the network are classifiedinto two distinct groups, one transmitting and the other receiving. Basestations or ANs that are in the same group cannot communicate with eachother over the same band. Hence, a mechanism for allocating compatibleradio resources across neighbor ANs is desirable.

3.6.9.1 Half-Duplex Constrained Resource Allocation

Assuming a tree topology of routes, a simple scheme for allocating radioresource to ensure that an upstream AN can communicate with a downstreamAN can be used. In this scheme, an upstream AN always take precedenceover a downstream AN in the decision on which radio resource is used forthem to communicate with each other. Specifically, starting from theroot node (e.g., an aggregation node) of a route tree, an upstream ANperiodically receives from a downstream AN its buffer occupancyinformation, along with the typical channel quality information. Basedon the received buffer and channel quality information, the upstream ANdetermines which radio resource (e.g., time slots) is used to transmitdata to or receive data from the downstream AN and signals such resourceallocation information to the downstream AN. Upon the receipt of suchresource-allocation information from its upstream AN and the bufferoccupancy information for its own downstream AN, the downstream AN thenallocates parts of the remaining resources for transmitting data to andreceiving data from its own downstream AN along the tree branch. Theprocess continues until all the leaves of the route tree are reached.

Although this resource-allocation scheme is by no means optimal, itprovides a simple and effective mean to cope with the half-duplexconstraint. However, to realize such scheme, the resource allocationschedules among neighbor ANs along a tree branch should be properlyoffset. Also, a new logical control channel may need to be defined toconvey buffer occupancy information from a downstream AN to an upstreamAN.

3.6.9.2 Reference Signal Offsets

The half-duplex constraint also imposes restrictions on the transmissiontiming of reference signals among neighbor self-backhauling ANs. Forexample, in order to maintain time-frequency synchronization amongneighbor self-backhauling ANs along a route or in order to performre-training of transmit and receive beam directions when necessary, eachAN should be able to listen to the reference signal transmitted by itsupstream AN. This implies that such reference signal cannot betransmitted simultaneously from neighbor ANs. One solution is to offsetthe subframe timing of neighbor ANs by an integer multiple of thesubframe period to allow the reference signals from different ANs to bestaggered. Similar to the resource allocation solution described above,an upstream AN along a route can again take precedence in selecting thesubframe timing offset and inform its downlink AN, which subsequentlyselects its own timing offset and propagates the offsets along theroute.

3.6.9.3 Impact of Propagation Delay

Due to differences in propagation delay, different UEs finish theirrespective downlink reception, and thus can begin uplink transmission,at slightly different timing. The need to transmit according todifferent timing advances to align timing at the receiver furtherincreases the problem. A guard period may need to be inserted at thetransition of downlink and uplink transmission to allow an UE to switchfrom reception to transmission. Alternatively, one may also lengthen thecyclic prefix of the first uplink time slot after switching fromdownlink transmissions.

3.7 Tight Integration of NX and LTE Evolution

NX is designed so that it benefits from coordination with LTE—at leastwhen both are deployed in the same operator's network. A future-proofsolution for the tight integration of LTE and NX is an important featurefrom the very first release, but also long term.

Realizing tight integration is approached by enabling seamlessconnectivity to LTE and NX for a given UE. Different architecturesolutions are presented in this chapter. A RAN-level integration withRRC/PDCP layer integration for LTE and NX is described in section 3.7.3.The challenges associated with a MAC-level integration (which wouldenable multi-RAT carrier aggregation) are also highlighted.

Section 3.7.1 contains some general motivations for LTE-NX tightintegration. Section 3.7.2 shows potential network scenarios where tightintegration is relevant, followed by device considerations in terms ofmulti-radio capabilities. In Section 3.7.3, different protocol solutionsfor the tight integration are described. In section 3.7.4, differentmulti-connectivity features like RRC diversity and user planeaggregation are presented. OAM aspects of the LTE-NX tight integrationare not covered.

3.7.1 Motivation

Tight integration fulfills 5G user requirements such as very high datarates by user plane aggregation or ultra-reliability by user or controlplane diversity. User plane aggregation is particularly efficient if NXand LTE offer similar throughput for a particular user so that theaggregation can roughly double the throughput. The occurrence of thesecases will depend on the allocated spectrum, the coverage and the loadof the two accesses. Ultra-reliability can be mandatory for somecritical applications for which reliability and low latency are crucialto maintain.

In addition to these, it is worth mentioning that the tight integrationalso provides enhancements to existing multi-RAT features (such as loadbalancing and service continuity) thanks to a RAN level integrationtransparent to the CN (less signaling). Service continuity, inparticular, is very desirable for early deployments, since it can beexpected that early NX deployments will comprise islands in a wider LTEcoverage.

The following focuses on characteristics that motivate support formulti-connectivity, for which LTE tight integration is one solution, toensure service continuity.

3.7.1.1 Challenging Propagation Conditions for NX in High FrequencyBands

In comparison with the current frequency bands allocated to LTE, muchmore challenging propagation conditions exists in higher bands, such ashigher free space pathloss, less diffraction, and higher outdoor/indoorpenetration losses, which means that signals have less ability topropagate around corners and penetrate walls. In addition,atmospheric/rain attenuation and higher body losses could alsocontribute to making the coverage of the new 5G air interface spotty.FIG. 119 shows an example of average SINR variations over a UE route inan urban deployment employing a large-array grid of beams, for a 15 GHz,comparing the optimal serving beam choice at all times with optimal beamswitching delayed by 10 ms. The route demonstrates some deeper dips thatindicate a sudden deterioration of the serving beam SINR due toshadowing, e.g., in “around the corner” situations. The serving beam SIRmay drop by over 20 dB within 5-10 ms. Such occasional drops areunavoidable at above 10 GHz and they should be handled seamlessly—Eitherby rapid beam switching, see section 3.5, or by relying on some form ofmulti-connectivity until the connectivity has been restored. The latteris a strong motivation for tight LTE/NX integration e.g., to provideservice continuity.

3.7.1.2 Massive Use of Beamforming

Beamforming, where multiple antenna elements are used to form narrowbeams to concentrate the energy, is an efficient tool for improving bothdata rates and capacity. Its extensive use, in particular at the networkside, is an important part of high-frequency wireless access in order toovercome the propagation challenges; see section 3.4. On the other hand,the reliability of a system using high-gain beamforming and operating inhigher frequencies is challenging, due to the high directivity andselectivity of large antenna arrays. Thus, coverage might be moresensitive to both time and space variations.

3.7.2 Network and Device Scenarios 3.7.2.1 Network Scenarios

The network scenarios for LTE and NX may be very diverse in terms ofcoverage and co-location. In terms of deployments, LTE and NX can beco-located (where the baseband is implemented in the same physical node)or non-co-located (where the baseband is implemented in separatephysical nodes with non-ideal backhaul).

In terms of coverage, LTE and NX may have essentially the same coverage,e.g., in a situation where LTE and NX are deployed co-located andoperating in a similar spectrum. This also covers the case where NX mayhave better coverage than LTE due to the usage of high-gain beamforming.Alternatively, NX may be deployed in a high frequency band which wouldresult in a spottier NX coverage. The different options are summarizedin FIG. 120.

3.7.2.2 UE Scenarios

UE scenarios are presented here, as certain UE types may be limited inthe kind of tight integration solutions they support. Characteristic ofthe different UE types is the number of receiver chains. It is expectedthat in 5G timeframe there will be UEs with dual radios, where eachradio has both receiver and transmitter (RX/TX) and that these can beoperated simultaneously. Such UEs will be able to be fully connected toLTE and NX at the same time without requiring time division operation onlower layers. From a specification point, tight integration is easiestto specify for this UE type, in the following referred to as UE type #1.However, from an implementation point of view, two transmitter chains(uplink) operating simultaneously introduces new challenges, includingthe need to split the limited TX power across the two TXs as well asintermodulation problems might prohibit dual UL TX in certain cases.Thus, there will also be UEs with dual RX but single TX, as these areeasier to implement, and these are referred to as UE type #2. Finally,there will be single-radio low cost UEs capable of both air interfaces,but only one at a time, referred herein to as UE type #3. The main focushas been on type #1 and type #2 UEs, as type #3 UEs cannot benefit asmuch on the features enabled by the tight integration. The UE types arehighlighted in FIG. 121.

3.7.3 RAN Architecture Supporting Tight Integration

In order to realize the tight integration of LTE and NX, the concept ofan “integration layer” is introduced. A protocol entity of the(multi-RAT) integration layer interacts with the RAT specific lowerlayer protocols (for NX and LTE respectively). The NX architecture isdescribed in section 3. In the following we show a summary of the prosand cons analysis for each integration layer alternative.

3.7.3.1 MAC Layer Integration

Using MAC as the integration layer means that the layers above would becommon to LTE and NX, as shown in FIG. 122. The main advantage oflow-layer integration is the potential of much tighter inter-RATcoordination features such as fast multi-RAT/multi-link switching andcross-RAT scheduling at the physical layer. MAC level integration wouldenable a Carrier Aggregation like operation between LTE and NX, allowingfor a very dynamic distribution of traffic even for short-lived flows.For instance, RLC retransmissions can be scheduled on any access,enabling quick recovery if one access fails. On the other hand,reordering of packets received over the different accesses would beneeded on either MAC or the RLC layer, which would delay the RLCretransmissions. Currently, the LTE RLC reordering timer can be tunedquite accurately due to the deterministic HARQ delays of the MAC layer,and this would no longer be the case for the more unpredictablereordering delays, which are depending on link quality and schedulingdecisions of the respective links.

A further benefit of MAC layer integration is that it can supportasymmetric UL and DL configurations. Poor UL NX coverage could be onedriver for such solutions, and would enable using available NX DLspectrum in combination with LTE UL when there is poor UL NX coverage(especially for higher frequencies) could be a strong motivator toenable MAC level integration. However, this would require carrying of NXphysical layer control information over the LTE uplink channels. Apartfrom mixing NX specifics into the LTE physical layer specifications,this would probably prove quite complex due to the different numerologyand round trip times of LTE and NX. For example, the staggered stop andwait HARQ of LTE uses a fixed timing, whereas the target for NX is tosupport varying timing in order to support more flexible deployments interms of baseband location.

The same argument applies to cross carrier scheduling between LTE andNX. This would cause strong dependencies in the specifications, andwould limit the possibilities for physical layer optimizations of eachaccess. The current stand of the internal NX concept is that the MACoperations for NX would differ quite much from LTE operations,complicating carrier aggregation like scheduling of UEs for LTE+NX.Therefore, if UL coverage turns out to severely limit the NX coverage, asolution with a NX DL carrier operating in high frequency could becombined with an NX UL carrier operating in low frequency, possiblymultiplexed with a LTE UL carrier using similar techniques as forNB-IOT.

3.7.3.2 RLC Layer Integration

RLC layer integration allows independent optimization of the MAC andphysical layer of each access, but still allows dynamic mapping of RLCtransmissions and retransmissions on the different accesses; see FIG.123. However, as for MAC level integration, the reordering timer of RLCwould need to be increased to cover reordering due to different packetdelivery times of the lower layers, which would slow down the RLCretransmissions. In normal conditions, RLC retransmissions are rare, andso is then the benefit of being able to reschedule a RLC retransmissionbetween accesses.

The interface between RLC and MAC is tightly connected in LTE, wheresegmentation is performed on RLC and scheduling (basically telling RLCthe requested RLC PDU size) is performed on MAC. The functional splitbetween RLC and MAC for NX is not yet set, but if the same split iskept, RLC level integration has the same limitations as MAC levelintegration when it comes to the support of backhaul.

3.7.3.3 PDCP Layer Integration

PDCP functions for the control plane are ciphering/deciphering andintegrity protection while for the user plane the main functions areciphering/deciphering, header compression and decompression using ROHC,in-sequence delivery, duplicate detections and retransmissions (used inhandovers). In contrast to the PHY, MAC and RLC these functions do nothave strict time constraints with the in terms of synchronicity with thelower layers. The main benefit of PDCP layer integration is that itallows separate optimization of the lower layers for each access. Adisadvantage is that this may require a fairly large remake of theMAC/PHY for NX, including new numerology and scheduling principles.

PDCP layer integration, illustrated in FIG. 124, also supports bothideal and non-ideal backhaul and can thus operate in both co-located andnon-co-located deployments. Still some of the same coordination featuresas for lower layer integration can be supported, e.g., load balancing,user plane aggregation, control plane diversity, coordinated RATscheduling, see. The difference is a lower granularity compared to lowerlayer integration. Here access can be selected per PDCP PDU and RLCretransmissions are access specific. One of the features that cannot beenabled by a PDCP integration is cross-carrier scheduling (as in carrieraggregation) where feedback of one access could be reported in anotheraccess.

One constraint with PDCP layer integration is that both uplink anddownlink connectivity is required for each access, which means thatasymmetric configurations with regard to UL and DL are not supported.

3.7.3.4 RRC Layer Integration

LTE-NX tight integration builds on RRC layer integration, illustrated inFIG. 125, to provide common control of connectivity, mobility,configurability and traffic steering between LTE and NX. Possibleimplementation alternatives of RRC for LTE-NX tight integration arediscussed in section 2.1.

3.7.3.5 Conclusion

In existing multi-RAT integration (e.g., between LTE and UTRAN), eachRAT has its own RAN protocol stack and its own core networks where bothcore networks are linked via inter-node interfaces. When it comes to theintegration between NX and LTE, enhancements have been proposed.

A first step towards this direction is a common CN integration. In thecase that each RAT has its own RAN protocol stack but the core network(and the CN/RAN interface) is common, new 5G core NFs can be used byboth LTE and the new air interface. This has the potential to reducehard handover delays and enable more seamless mobility. On the otherhand, potential multi-RAT coordination is limited. Based on the designcharacteristics of NX and the analyses for the different alternativesfor the integration layer, the integration is placed at PDCP/RRC layers.

3.7.4 Tight Integration Features

In this section it is described which features can be realized by thesolution for the tight integration. A summary of the features is shownin FIG. 126, assuming an RRC implementation based on a common RRC withthe LTE's RRC extended to cover NX new procedures and acting as sort ofMeNB (see section 2.1).

3.7.4.1 Control Plane Diversity

RRC level integration for LTE and NX as described in section 2.1provides a single point of control at the network and UE for dedicatedsignaling. To improve signaling robustness, messages from this point canbe duplicated at the link layer, with copies of the RRC messagetransmitted via separate links to UEs with dual radio (UE type #1). Inthe preferred architecture, this split is performed at the PDCP layer,so that PDCP PDUs are duplicated at the transmission point and each copysend over individual link to the UE, and duplicate detection isperformed in the receiving PDCP entity to remove redundant PDCP PDUs.

The feature can be applied to both uplink and downlink transmissions. Inthe downlink, the network may decide to use one link or another. Onesignificant aspect of the feature is that no explicit signaling would beneeded to switch the link which imposes that the UE transceiver shouldbe capable of receiving any message on any link. The main benefit ofthis feature is to provide additional reliability without the need forexplicit signaling to switch air interface, which might be important tofulfill the ultra-reliability requirements for certain applications inchallenging propagation conditions where the connection on one airinterface is lost so quickly that no explicit “switch signaling” couldhave been performed.

The feature could also be used, for example, during mobility procedureswhere NX links could degrade so quickly that the fact that the UE canjust use the LTE link without the need to any extra signaling isbeneficial. With diversity, the UE could send measurement reports viaboth LTE and NX so that up to date measurements are available at thenetwork for handover decisions. In the same scenario, handover commandscould be sent by both LTE and NX.

3.7.4.2 Fast Control Plane Switching

Fast control plane switching is one possible alternative to the controlplane diversity, which relies on RRC level integration and which allowsthe UE to connect to a single control point via NX or LTE and switchvery fast from one link to another (without requiring extensiveconnection setup signaling). The reliability might not be as high as inthe Control Plane Diversity and additional signaling would be needed toenable the link switch compared to Control Plane Diversity. The solutiondoes not allow simultaneous reception/transmission. On the other hand,one advantage is that the solution would work for all UE types definedin section 3.7.2.2.

These two solutions can be seen as alternatives but can also becomplementary, where the first solution could be used only in criticalscenarios to improve reliability. They can be seen as differentoperation modes configurable at the UE depending on the differentprocedures/messages or UE types.

3.7.4.3 UL Control Plane Diversity and DL Fast Control Plane Switching

Some potential issues have been identified for the fast controlswitching solution, e.g., the RLF handling. Then, as a more experimentalalternative, a hybrid with the Control Plane Diversity has beenproposed. This hybrid comprises a Control Plane Diversity in the Uplink(UE is capable of sending RRC messages via NX and/or LTE while thenetwork is prepared to receive these messages from either/both accesses)and a Fast Control Plane Switching in the Downlink, where the UE isinformed by the network which access it should listen to receive RRCmessages and the network sends only via one access.

The solution can be considered as a fallback in the case the ControlPlane Diversity solution is too complex e.g., in the case of UE type #3,which could be relaxed in the case of Control Plane Switching. Note thatin case the two accesses are not tightly synchronized or aretransmitting in different bands, the UE may need to re-acquiresynchronization every time it needs to transmit over the other access,which could consume some time making it less suitable for some criticalprocedures. Another challenge to enable the usage of the feature by UEtype #3 is the fact that it takes even longer is to reliably discoverthat the UE failed on the “first” access and then to “find” the suitableconnection on the other access. One way to address that issue is toconfigure the UE to constantly monitor a secondary access in order to beprepared. A possible drawback of this is that it can consume extra UEbattery and enforce some additional DL transmissions on the NX side.

3.7.4.4 User Plane Aggregation

User plane aggregation has two different variants. The first variant iscalled flow aggregation which allows a single flow to be aggregated overmultiple air interfaces. Another variant is called flow routing where agiven user data flow is mapped on a single air interface, so thatdifferent flows of the same UE may be mapped either on NX or LTE. Thisoption requires a mapping function of the flows to different bearers inthe core network.

The benefits of user plane aggregation include increased throughput,pooling of resources and support for seamless mobility. The featureworks only for UEs of type #1, if PDCP layer integration is assumed.

3.7.4.5 Fast User Plane Switching

For this feature, rather than aggregating the user plane, the UE usesonly a single air interface at a time, relying on a fast switchingmechanism between them. Apart from providing resource pooling, seamlessmobility and reliability, a main advantage is that it applies for UEtypes #1, #2 and #3, where only one access is used at a time. It isexpected that fast switching may be sufficient in a scenario where oneaccess provides significantly higher user throughput than the other,whereas user plane aggregation provides additional significantthroughput gains in scenarios where access performance is more similar.

3.8 Operation in Shared Spectrum

It is important that NX can be deployed in all frequency bands that aremade available for 5G, including frequency bands allocated for sharedoperation. As a consequence, NX system should be able to share spectrumwith other NX systems and/or different technologies, such as LTE andWi-Fi, on the same carrier. Focus is on TDD operation assuminghalf-duplex transmission, but full duplex is possible and enables a moreaggressive sharing mechanism.

3.8.1 Sharing Scenarios

FIG. 127 illustrates a summary of spectrum types and usage scenarios forNX systems. Besides licensed dedicated use, it is clearly seen thatspectrum sharing is commonly divided into the following categories:

-   -   Vertical sharing refers to spectrum sharing between systems of        different priority (e.g., primary and secondary), with unequal        rights of spectrum access.    -   Horizontal sharing is sharing between systems that have the same        priorities in the spectrum, where different systems have fair        access rights to the spectrum. If the sharing systems in the        spectrum adopt the same technology, it is called homogenous        horizontal sharing, e.g., inter operator sharing in the same        carrier/channel; otherwise heterogeneous horizontal sharing,        e.g., LTE sharing with Wi-Fi. Homogenous horizontal sharing can        also be applied in licensed mode between different operators        typically using the same technology.

NX is expected to cover 1˜100 GHz spectrum ranges, where the mostpromising shared spectrum lies in the following categories:

-   -   Case A: Unlicensed bands such as 5 GHz and 60 GHz which are        already available for network deployment. This is the most        typical case for sharing of spectrum and very promising for user        deployed scenario (e.g., enterprise) since there is no need for        user to coordinate with operators when operating in unlicensed        band;    -   Case B: Co-primary licensed bands with inter-operator horizontal        sharing especially above 30 GHz which is proved to have benefit.        Spectrum efficiency may be improved a lot by introducing        inter-operator sharing especially for low interference        environment with massive MIMO in NX;    -   Case C: LSA bands operation as secondary systems without or with        horizontal sharing. Vertical sharing techniques could open the        door for 3GPP systems to use more spectrums and make global        harmonization of spectrum easier. Similarly, inter-operator        horizontal sharing can be valid as well in LSA bands.

3.8.2 Motivations and Requirements

Current 2G, 3G and 4G systems mainly use licensed dedicated spectrum fornetwork deployment. However, NX systems aiming for 5G with massivebandwidth need significantly more spectrum than today and it is hard tofind enough bands to achieve this by using licensed dedicated spectrum.Besides, NX systems are more likely to serve new application scenariossuch as enterprise, which favor shared spectrum operation. Therefore,shared spectrum operation plays an important complementary role to usespectrum for NX systems.

In shared spectrum, where multiple systems can coexist and interferewith each other, there is a need for coexistence rules. In general,there is no protection that a user can expect from interference whenoperating in the unlicensed regime, but intentional radiators engaged incommunication must follow rules designed to minimize interference toother devices using the band. The FCC has devised such rules for faircoexistence in unlicensed bands, as has CEPT in association with ETSI.Current regulations typically provide a spectral mask which limits thetotal power and power spectral density (PSD) that each transmitter canuse. In addition, there are derived protocols that are sometimes quiteliberal in the extent to which a transmitter can gain access to thechannel, and at other times are more restrictive; the coexistenceprotocols typically followed in the 5 GHz band allow the liberalapproach in the US and restrict users to following listen-before-talk inEurope.

The sharing problem is itself not new, as numerous devices on the 2.4GHz and 5 GHz unlicensed bands already behave in a manner that isunfriendly to neighboring devices. Up to now, the FCC rules have beenband dependent and technology-neutral. In 2.4 GHz and 5 GHz bands Wi-Fiis established as a dominating technology most often using some sort ofListen-before-talk mechanism (LBT) to enable fair coexistence and globalrelevance. This has established LBT as a de facto method for providingfairness. New technology such as licensed assisted access (LAA) for LTEhas also adopted LBT to enable fairness. The IEEE 802.11 standard alsoproposes coexistence techniques in the new ‘ad’ amendment for 60 GHz,but common use of that band may not employ LBT uniformly, as it isexpected that spatial isolation between users may often make activesensing of the channel unnecessary. Recently, the FCC has proposedexpanding the 60 GHz band from its current 57-64 GHz to included 64-71GHz as well.

New bands may be expected for shared spectrum use elsewhere in thefuture and NX should be able to operate within such spectrum. It remainsto be seen how the regulators will handle fair coexistence whenembracing new technology and new bands. For vertical sharing, the mainwork is in the regulatory bodies to establish coordination interfacewith primary systems, which has small impact on the radio design for NXsystems, e.g., geolocation database (GLDB) support. So the followingfocuses on how NX systems are designed to solve horizontal sharingbetween different operators or systems. Unlicensed bands such as 2.4 GHzand 5 GHz are already used by a number of access technologies, e.g.,802.11(Wi-Fi). Currently, licensed assisted access (LAA) is beingdeveloped in 3GPP to make LTE operate in unlicensed bands and coexistwith Wi-Fi systems. LAA for LTE has the potential to offer bettercoverage and higher spectral efficiency comparing to Wi-Fi. Thismilestone to deal with horizontal sharing for 3GPP technology lays asolid base for NX operation in shared spectrum.

NX has some characteristics that ease operation in shared spectrum ascompared to LTE:

-   -   Smaller granularity in time domain (see 2.3.2), e.g., 62.5 μs        subframe.    -   Flexible HARQ scheme; no strict timing on ACK/NACK and        retransmission (see 2.2.8).    -   Flexible TDD (see 2.3.2.1); UL transmission is scheduled and is        allowed in any subframe.    -   Full duplex operation.    -   Contention-based uplink data transmission (see 2.2.6).    -   Massive MIMO with high-gain beamforming (see 3.4) provide        isolation and reduces interference in many cases. However,        high-gain beam forming may also bring challenges to coexistence        mechanism like Listen-before-talk. Details are elaborated in        later sections.

3.8.3 Coexistence Mechanism for Horizontal Sharing

Listen-before-talk (LBT) is the most flexible tool to support horizontalsharing for the following reasons: a) distributed structure withoutneeding information exchanges between different networks or nodes; b) itmay realize the coexistence support with different operators or systemssimultaneously. Section 3.8.3.1 introduces LBT concept with high-gainbeamforming and addresses possible problems brought by massive MIMO incombination with LBT. Then, in section 3.8.3.2, a Listen-after-talk(LAT) mechanism is introduced to solve some problems. Finally, section3.8.3.3 summarizes the application scenarios for both mechanismsaccording to analysis.

3.8.3.1 Listen-Before-Talk with High-Gain Beamforming

An important idea of LBT is that the source node (SN) listens to checkthe channel status before it actually transmits to destination node(DN). In other word, the default mode of LBT for SN is ‘not to send’ anddata is sent only when it is confirmed that the channel is available bylistening. Here ‘available’ means that the planned transmission willneither interfere nor be interfered by current ongoing transmission. Sothe assumption behind this is that the sensed power at SN siderepresents the interference power at DN side. However, when the sensedpower at SN side is much smaller than interference power at DN side, thehidden node problem may occur, where the channel is considered availablebut actually occupied. In contrast, the exposed node problem may occurwhen sensed power is much larger than interference power, where thechannel is detected busy but is actually not occupied. In current Wi-Fior LAA systems for LTE, these problems already exist, but they are notso severe and can be tuned by setting feasible detection threshold. Theprobability of such problems occurring when using LBT is acceptableaccording to evaluations and practical applications in current Wi-Fi orLAA systems for LTE. For LBT, how long time needs to be sensed for eachtransmission can also be considered. For this purpose, a back-offcounter is introduced for LBT. The counter is generated randomly when SNwants to transmit data and decreases if the channel is sensed idle. Whenit expires, SN regards the channel as idle and could start to transmitdata in the channel.

For NX systems with large antenna arrays, high-gain beamforming isavailable for data transmission. This exacerbates the hidden- andexposed node problems. Due to high-gain beamforming, the sensing powerphase is done with a directional beamforming pointing towards thedirection the node wants to transmit. In this case, differently orienteddirections may result in different receiving powers.

FIG. 128 illustrates examples of the hidden node and exposed nodeproblems. In FIG. 128a , AN1 is transmitting data to UE1 and AN2 islistening. Since it is not in TX coverage of AN1, AN2 considers thechannel is available and thus starts to transmit data to UE2. Butactually UE1 is interfered by AN2's transmission due to it is in AN2'sTX coverage. A reason behind this is that sensed power at AN2 is muchsmaller than the interference power at UE1 side due to directiondifference. In contrast, the exposed node problem is illustrated in FIG.128 b.

More antennas (e.g., 100 antennas at AN side) result in less correctLBT, with more severe hidden node problems and exposed node problems.Here, ‘correct’ means ‘channel detected as busy, actually interfered’and ‘channel detected as available, actually not interfered’. This canlead to performance degradation on both average system throughput andcell-edge user throughput.

Request to send/clear to send (RTS/CTS) handshaking mechanism isproposed in Wi-Fi systems to solve hidden node problem brought byphysical carrier sensing. It is an additional method to implementvirtual carrier sensing over physical carrier sensing. When physicalcarrier sensing indicates the channel is idle, data SN transmits RTS toDN and then DN responses one CTS to accomplish handshaking. Neighbornodes hearing RTS and CTS defer their transmission so that hidden nodeproblem doesn't exist. However, this makes exposed node problem moresevere and also introduces more overhead for RTS/CTS transmission beforedata transmission. Considering the problems in high-gain beamformingcase, exposed node problem is already a problem and RTS/CTS canpronounce it. Besides, interference probability is much smaller inhigh-gain beamforming case which means a lot of RTS/CTS overhead beforedata transmission is unnecessary. For these reasons, traditional RTS/CTSis not a good solution to solve hidden node problem and exposed nodeproblem in high-gain beamforming case.

3.8.3.2 Listen-After-Talk (LAT) Mechanism

A so-called listen-after-talk mechanism is introduced to address theabovementioned hidden- and exposed-node problem in massive antennascase. A reason to have such severe problems for LBT is a largedifference between sensed power at SN side (e.g., AN2 in FIG. 128) andinterference power at DN side (e.g., UE1 in FIG. 128) in high-gainbeamforming case. Thus, LAT involves the receiver to sense the channeldirectly. Another motivation for LAT is low interference situations,where there are fewer collisions for naive direct transmission. For thisreason, LAT adopts opposite logic compared to LBT as follows: thedefault mode for transmitter is ‘to send’ and data is not sent only whenit is confirmed that channel is occupied by interfering transmissions.An important idea is that the SN transmits anyway when data packetsarrive and then solve collision detected by DN according to coordinationsignaling.

To address LAT clearly, the following definitions are assumed:

-   -   Idle time is assumed after continuous data transmission. This is        reasonable for unlicensed band since there are always channel        occupation limitation rules, e.g., the SN must stop transmitting        and enter idle state after contiguous transmission time exceeds        a given threshold;    -   Notify-To-Send (NTS) message: This message can be transmitted by        SN or DN, including the link information which will transmit        data and expected occupation time duration;    -   Notify-Not-To-Send (NNTS) message: This message is transmitted        from DN, telling its SN not to transmit data in indicated        duration.

A short description of procedures for SN and DN is given here. First,the listening function at DN side is triggered when it detectsinterference and fails to receive the data. Then the DN of victim linkcoordinates the data transmission with SN of the aggressor link(s).Finally, the coordination is performed in idle time of aggressor link.One example is shown in FIG. 129, where AN2→UE2 is interfered byAN1→UE1. When UE2 fails to decode the data, it starts to look for theidle period of aggressor link and send NTS message towards AN2direction. Since UE2 is interfered by AN1, AN1 can receive the messageas well and then defer the transmission as NTS indicates. Besides, NTSalso indicates when AN2 will stop transmission and listen, the idleperiod of AN2→UE2. Then AN1 transmits NTS that can be received by UE2.Finally, NNTS is relayed by UE2 to let its transmitter AN2 know whichresource is occupied by aggressor link and not transmit. By this scheme,the transmission of this interference pair (AN1-UE1 and AN2-UE2) iscoordinated in distributed way to transmit data by turns.

3.8.3.3 Summary

Both LBT and proposed LAT scheme are aiming to solve the interferencebetween operators or systems to achieve good coexistence. So taking intoaccount their different design ideas. Table 16 summarizes therequirements and possible application case as follows:

TABLE 16 Comparison between Listen-before-talk and Listen-after-talkmechanism Coexistence Listening scheme Structure node Signaling ScenarioLBT distributed SN only Optional Small to middle antenna gain LATdistributed Both SN and Mandatory Large antenna DN gain

From the above comparison, LAT scheme involves RX's listening and thussignaling between data source node (SN) and data destination node (DN),e.g., NTS and NNTS. For LBT scheme, only data SN is listening whileoptional signaling may be adopted to solve the hidden node problem. Inother words, RTS/CTS handshaking may be standardized in Wi-Fi protocol.However, RTS/CTS can't solve exposed problem which may severely degradefrequency reuse in massive antenna case.

LBT can work well to achieve coexistence using moderate antenna gain (ANwith less than 16 antennas). However, for high antenna gain case,alternative solutions, including LAT, may be used.

3.8.4 LBT-Based Data Transmission

This section describes how to incorporate LBT in the NX frame structurefor physical data and control channels defined in section 2.3.3. For thepurposes of this section, it is assumed that both DL and UL datatransmission are subject to LBT. This is motivated by the assumptionthat LBT is needed for operation in both 2.4 GHz and 5 GHz bands. Fornew frequency bands at higher frequencies where high antenna gain isexpected to be used, other sharing mechanisms such as LAT may be used.For NX, data transmission-related channels are defined as introduced in2.3.3, e.g., the physical control channel (PDCCH) and physical datachannel (PDCH). PDCCH is used to schedules PDCH which could accommodateeither DL or UL data.

To reduce uplink transmission latency, cPDCH was introduced to enablecontention-based access, as described in 2.2.3. With cPDCH, asemi-persistent grant that may be assigned to multiple UEs isintroduced. Referring to the discussion in section 2.2.6, cPDCH is usedfor transmission of initial uplink data in a contention way. In section2.2.6 there is also a description of how an LBT mechanism may be addedto cPDCH for access in dedicated spectrum, to further improveperformance.

3.8.4.1 DL LBT-Based Data Transmission

For DL data transmissions, there are two different kinds ofopportunities to transmit DL data: PDCH scheduled by PDCCH, or one couldapply contention-based resource handling similar to what has beendevised for DL using cPDCH. In this section, these access methods haveto be accompanied with LBT.

The principle of using PDCH for LBT-based DL transmission of data isillustrated in FIG. 130, which illustrates a PDCH-carried DLtransmission example, at the eNB side. First, the eNB starts to sensethe channel M symbols before PDCCH. Then, the back-off mechanism isperformed to determine if it is OK to transmit data by physical carriersensing. When the randomly generated back-off counter expires, the eNBinserts reservation signal to occupy the channel until PCCH boundary. Ifthe carrier is determined to be idle, the eNB schedules the datatransmission by transmitting PDCCH to the UE including a DL assignmentindicator (all UEs that expect to receive data on a specific resourcehas to what PDCCH to monitor). Finally, the eNB transmits the dataaccordingly. PDCCH and PDCH are co-located in the continuous resource asmentioned in section 2.3.

In Section 2.2, cPDCH is discussed for UL transmission only. Here weshow that the cPDCH can also be used for LBT-based DL transmission.Before DL transmission using cPDCH, the eNB needs to configure UEs tomonitor shared resources to detect if there is cPDCH transmissionsintended for them. If DL data to these configured UEs arrives, the eNBstarts to sense the channel at before these resources and performListen-before-talk, as illustrated in FIG. 131. (Note that a longerrandom back-off counter as compared to what is used for UL data providespriority to LBT based cPDCH-carried UL data). When determined idle, eNBsends DL data packet with special format as compared to PDCH-carried onein cPDCH immediately. The whole special packet includes preamble andheader comprising of multiple fields (e.g., data duration, ID of DN andetc.) before the DL data payload so that the UE can know the beginningand end of the data designated for it.

Using cPDCH in DL in this way is similar in some respects to how Wi-Fitransit data in DL. However, the cPDCH resources are configured by MAC.So, it could be seen as contention MAC over scheduled MAC. When lowload, resources for cPDCH can be configured large to have low latencyfor both UL and DL; when medium and high traffic load, the resources forcPDCH can be set small, to have more scheduling MAC.

3.8.4.2 UL LBT-Based Data Transmission.

For UL data transmission, there are also two options for LBTtransmission: PDCCH-scheduled PDCH-carried UL, and cPDCH-carriedcontending UL. For UE-initiated transmission on PDCH, the UE first sendsan UL scheduling request using cPDCH on a shared resource, and thenPDCCH is used to inform the UE when it can transmit. To reduce delay,the cPDCH can be used to carry data directly, as outlined in section2.2.6.

First, a cPDCH resource should be configured for the UE. Then, the UEwith UL data starts to sense the channel at cPDCH staring boundary, asillustrated in FIG. 132, which shows an example of UL data transmissionin cPDCH. LBT is performed at UE side until a back-off counter becomesexpired. A shorter random back-off timer generation window is used,compared to that for DL data, to prioritize its transmission. When thechannel is determined as idle, UE sends the UL data including bufferstatus report in cPDCH. Note that transmission in cPDCH is not limitedto initial UL data.

Another UL data transmission option is PDCH-carried scheduling UL data.It is assumed here that UL scheduling request and buffer status reportare already available at the eNB. There are two steps to perform thiskind of transmission, as shown in FIG. 133, which shows an example of ULdata transmission in PDCH. First, assume that the contention for PDCCHtransmission is successful at eNB side. Then, the eNB transmits PDCCHincluding an UL grant scheduling grant for the UE. Then, the UE detectsPDCCH and prepare to send UL data when LBT succeeds, after the LBTperiod shown in FIG. 133.

One problem with PDCCH scheduled PDCH-carried UL data is that the ULgranted resource is not used if LBT at UE side fails, which results inresource waste. One solution to this problem is to apply grouped grantopportunity for different UEs in a partly overlapping resource. Forexample, as shown in FIG. 134, which illustrates the coupling of a DLand UL grant, one DL grant is scheduled to start shortly after the ULgrant resource opportunity. In this way, the eNB first decodes in thefirst subframes: If CRC checks there is UL data, and the eNB can proceedto receive the rest of the UL data transmission; otherwise, the eNBstarts DL LBT procedure to initiate DL transmission. Note that the UEsgranted in overlapping resource are preferred to be carefully selectedto increase the probability of successful contention for the resource.For example, if UEs with large distance in one cell is selected, it isreasonable to assume that they have different channel state. Then, aslong as at least one of them is successful, the resource would beoccupied.

3.8.5 LBT-Based Transmission for System Plane

To support stand-alone operation in shared spectrum, transmission ofsystem plane (see section 3.2) should also be considered. As introducedin section 2.3.4.1, periodic system signature index (SSI) and accessinformation table (AIT) transmissions are fundamental to UE initialaccess. However, shared spectrum operation may bring uncertainty of theperiodical transmission and thus their transmission under LBTconstraints needs to be carefully designed. The details are given in thefollowing subsections.

3.8.5.1 SSI Transmission

In NX system design for licensed band, SSI is a strict periodic signalsequence transmission (e.g., every 100 ms), to provide synchronization.Further, the sequence is allocated in a pre-defined group ofsubcarriers, e.g., a small number of possible positions of the workingcarrier.

In shared spectrum band operation, a much larger number of candidate SSIsequences are desirable, to reduce the possibility that SSIs fromdifferent un-coordinated network nodes are different. On the otheraspect, LBT should be performed in the process of SSI transmission. Inparticular, the eNB starts listening a certain time (e.g., 4 subframes)before a periodic SSI transmission time. When the randomly generatedback-off counter expires, a reservation signal is inserted until SSItransmission time, to avoid others jumping in. In order to prioritizeSSI transmission compared to data transmission, a shorter contentionwindow than for data transmission is used, e.g., Q=8 for SS and Q=20 fordata, where [0, Q] is the range for random back off counter. Since SSItransmission is only located in a small number of possible positions inthe carrier, DL data transmission or dummy signals are transmitted inother subcarriers at the same time, as shown in the SSI transmissionexample illustrated in FIG. 135, so that other listening devices canregard this carrier as busy or occupied by energy sensing. AIT or otheruseful system information could be put here as well.

However, it is possible that LBT fails at the transmission time of SSI.To alleviate such problem, multiple candidate positions for SSItransmission can be predefined, e.g., the three dashed resource blocksin FIG. 135. For the same SSI, additional sequences are used to indicatethe transmission time offset. eNB still starts to monitor the carrierbefore the first candidate position. If LBT fails until starting pointof the first one, eNB continues to monitor the channel and seeksopportunity to transmit SSI in the second or third candidate positionswith different sequences. Note that different sequences are used toindicate the predefined offset in different position. One example isshown in FIG. 136, which shows SSI transmission contention: NX operator1 (OP1) and operator 2 (OP2) have different back-off counters. When OP1back-off counter expires, the eNB transmits SSI. Then OP2 considers thischannel as busy and stops back-off. When SSI of OP1 ends, OP2 finish therest back-off time and transmit.

3.8.5.2 AIT Transmission

In a manner similar to that used with SSI transmissions, the eNB startsLBT before periodical AIT transmission (e.g., every 100 ms). First, itis assumed that one or several sequences along with AIT are used for UEsto detect time position of AIT transmission, as introduced in section2.3.3.4. Then, one predefined transmission window is introduced to allowAIT transmission when LBT succeeds. This transmission window (maximumoffset) should be indicated to UE via signaling, for scanning AITblindly. As discussed in section 3.2.2.2, SFN/Timing information is alsoprovided in the AIT content. Here, SFN/Timing indicates the time in thegranularity of 10 ms in NX, for example, instead of 1 ms in LTE.However, AIT transmission offsets may occur, as shown in FIG. 137, suchthat one additional field is desirable to indicate a millisecond-level(less than 10 ms) offset. Finally, the real AIT transmission time is acombination of SFN/Timing and the millisecond-level time offset.

3.8.5.3 UE Access Procedure

The UE searches for SSI and AIT to update system information needed forinitial access. After power up, UE scans SSI first to know which nodecan be accessed. From SSI detection, UE can get coarse synchronizationby adjusting SSI transmission time offset indicated by the SSI sequenceID. Simultaneously, the UE can know SSI from the detected sequence. Iflocal AIT doesn't have information on needed information for detectedSSI, UE needs to scan AIT by detecting the self-contained sequence. Thereal global time is calculated by adding global time field and timeoffset for further use. Referring to section 3.2.2.2.2, the UE accessprocedure is updated with offset indication in shared spectrum, as shownin FIG. 138, which illustrates the UE access procedure in sharedspectrum. A difference (bold text in FIG. 138) from licensed operationis that synchronization offset is obtained from SSI detection, and thussynchronization implies further processing by complementing the detectedoffset. Further, the accurate global time from AIT detection should beobtained by considering AIT offset field as well, which may be used forSSI scanning.

3.9 Self-Organizing Networks

Self-organizing network (SON) features were listed among the LTErequirements, and some important concepts, functions and proceduressignificantly facilitated the introduction of new nodes as well asoptimization of the operation of existing nodes. Therefore, it isnatural for NX to provide at least a comparable level of automation.

This section describes some fundamental automation concepts for NX,mainly targeting the early deployment and operation phases. The textalso comments on the differences from LTE. LTE BS automation was to alarge extent influenced by the design choices implying that BSsbroadcast fixedly allocated signals and identifiers. Such broadcastsserved as a basis for a wide range of functions, including idle modemobility, initial access, frequency selective channel estimation,mobility measurements, positioning etc. As described in the presentdocument, the NX design avoids such broadcast as much as possible.Furthermore, as discussed in Section 3.10, it is desirable to avoidbroadcast of a fixed sequence or identifier over time from the same BSor antenna configuration. Instead, it is possible to operate an NXnetwork in a mode (obfuscated mode), where transmitted sequences andidentifiers from an antenna configuration are changed regularly. Thesedesign choices have an impact on NX RAN SON.

The introduction of a new base station in an NX network is subject toseveral management and automation tasks to ensure a smooth introduction.These tasks are listed in sequence in FIG. 139, and are discussed inmore detail below.

-   -   Site planning. Traditionally, base station sites are planned.        The planning includes establishing a leasing agreement with a        landlord and deciding an appropriate site location. Since NX        introduces new concepts and features, also the site planning        procedure is affected. Potentially, this step can be omitted in        detail, in favor of a more ad hoc deployment procedure, where        the BS is placed at an appropriate location during a site visit.    -   OAM system connection establishment. Once the BS is deployed, it        needs to establish contact with the OAM system to confirm the        deployment and to associate the BS hardware with the planned        site. The OAM system also has the possibility to upgrade the BS        software and obtain system parameters. The BS may also retrieve        information about how to establish backhaul and fronthaul to        realize transport network connections, core network connections,        inter-basestation connections, etc.    -   System access establishment. The system plane is configured to        provide UEs with system access. A new base station needs to be        included in a set of base stations providing system plane        access, and the system plane needs to be tuned accordingly.    -   BS relation establishment. By automatic establishment of        inter-BS relations, the infrastructure is capable of        establishing relations between the nodes that needs to interact        and exchange information.    -   Beam relations establishment. With beam based communication        between a base station and a UE, the network can benefit from        establishing relations between beams at different transmission        points and also between different beams from the same        transmission point.    -   Mobility robustness optimization. The NX active mode mobility is        supported by the transmission of beam-formed mobility reference        signals. The mobility procedure tuning includes deciding when it        is appropriate to initiate mobility measurements, and when to        initiate the handover procedure.    -   Self-optimization and healing. This section only addresses a        limited set of SON procedures, and there are other procedures        such as identity management, load balancing, coverage and        capacity optimization, handling of disruptive events etc.

3.9.1 Site Planning, OAM System Connection Establishment and SystemAccess Establishment

Despite ambitions to make radio network node configuration andoptimization extensively automatic, site planning involves manual worksuch leasing agreements with landlords, and providing at least a set ofcandidate sites where site deployments can be realized. Part of the siteplanning can also be automatic, for example to select sites fordeployment among a set of site candidates, and to define some basicconfiguration parameters such as base station type and capability,transport network type and capability, maximum transmission power, etc.The configuration can be separated into hardware configuration andparameter configurations. The latter includes pre-configurations ofradio functions, identifiers, sequences, security, base stationrelations, inter-base station connections to be established etc., wheresome parameter configurations can be seen as optional.

The scope of the configuration can vary depending on the level ofdistributed automation of certain parameters and procedures, if thisautomation is conducted centrally, or if the parameters arepre-configured based on planning. It also depends on the considereddeployment strategy (see also section 3.2), for example:

-   -   A. each base station (a traditional base station or a cluster of        transmission points connected with good backhaul, sharing the        same interface to other nodes) is configured with its specific        system access configuration, and thereby a base station specific        SSI    -   B. system access configuration is shared between base stations        in the same region, and the backhaul characteristics is very        different between different base stations, and might not be        known before the deployment.    -   C. System access configuration is shared between base stations        of the same type, which for example can mean that macro base        stations are configured with one SSI, and micro base stations        with a different SSI.

In deployment strategy A, each base station provides its specific systemaccess, and some preferably automatic planning can configure the systemaccess. In case base stations in the form of clusters with transmissionpoints, these may already initially have some pre-configuredinter-transmission point connections within the cluster to enablecoordination of receptions and transmissions. Once deployed, the systemaccess configuration can be automatically reconfigured to adapt to thelocal conditions. These local radio conditions can be learned over time,based on a combination of UE and BS measurements.

In deployment strategy B, the ambition is to provide regional systemaccess. Therefore, the system access configuration can initially beplanned just as in strategy A. Once deployed, base stations can bereassigned to new system access regions based on the local radioconditions. These local radio conditions can be learned over time, basedon a combination of UE and BS measurements. The backhaul can be veryvarying and subject to varying latency, limiting coordinationcapabilities.

In the event that NX is deployed in an area where there already exists alegacy system, then existing logical models (neighbor relations,tracking area configurations, random access procedure statistics) can beused to assign the base station to a system access region (strategy B)either in the planning phase, after establishing the connection to theOAM system, or once the relation between the new NX base station and thelegacy network has been established.

Similarly, with NX deployed with different base station types in mind,each type can be associated to the same system access configuration(strategy C). This is reasonable for example if the system accessconfiguration should be related to the transmission power of the basestation.

One alternative is to deploy new base stations with a BS specific systemaccess (strategy A) from a set of system access configurations only usedfor newly installed base stations. Once sufficient knowledge about thelocal conditions has been established, the base station is assigned to asystem access region (strategy B).

Similarly, the tracking area configurations also can be subject to(automatic) planning prior to site installation, centrally determined aspart of the initial OAM interactions, or distributedly reconfiguredafter the base station has been deployed. The tracking area may bedependent of existing tracking area configurations in legacy networks,and may be related to the system access regions.

In case obfuscated operations is considered (section 3.10.3), where somebase station reference sequences and/or identifiers are obfuscated, thebase station needs to establish a connection to the positioningmanagement entity (PME). In this way, the base station obtainsencryption details, validity times, etc., about such transmissions. Someof these configurations are for common positioning functions, and somefor dedicated positioning functions. Random access configuration andoptimization can be seen as two parts, first the random access parameterconfiguration of the system access needs to be tuned in relation to theconfiguration of the system access in adjacent regions, and second therandom access handling within the system access region needs to beestablished.

For random access parameter configuration, the strategy can be that thebase station or the OAM system gathers random access statistics based onbase station measurements (no of received system access preambles, no ofsuccessful/failed system access procedures, no of received node-specificrandom access preambles, etc.), and/or UE measurement reports associatedto the random access procedure (number of transmitted system accesspreambles and node-specific random access preambles, number of procedurefailures due to contention, number of preambles transmitted at maxpower, etc.).

Once the system access is configured and the base station isoperational, the base stations and nodes of the system access regionneed to establish knowledge of node reception and transmission coverageoverlaps within the system access region and between system accessregions. The parameter configuration and tuning aims at locally uniquesystem access configurations, which means that the set of configuredsystem access preambles and node-specific random access preambles, aswell as the related resources in time, frequency and space can bealtered due to overlaps with adjacent system access regions.

For deployment strategy A and B, such overlap statistics can also beused to understand which beams and nodes within the system access regionthat all are likely receive a preamble from a UE, and also which arecapable of transmitting a response to such a UE. Equally important is toestablish which beams and nodes with the system access region that arenot likely to receive the same preamble from a specific UE, or areincapable of transmitting a response to the same UE. This knowledge maybe formalized as reception and transmission RA relations, as well asreception and transmission RA non-relation.

FIG. 140 illustrates an example of such overlap, where two differentsystem access regions have an overlap and needs to align the systemaccess configurations. Furthermore, within the system access region withSS1, nodes B1 and B2 have a RA relation (both reception and transmissionfor simplicity) as concluded based on statistics associated to UE 1 andsimilar, while nodes B1 and B2 have a RA non-relation as concluded basedon statistics associated to UE 1 and UE2 and similar. In case ofdeployment strategy B, such relations can be used to coordinate RAresponses, uplink configurations and contention handling between nodes.For deployment strategy C, the relations may instead be used whencoordinating node-specific RA preambles and resources on a longer timescale.

3.9.2 Base Station Relation Establishment

Despite advanced radio network planning tools, it is very difficult topredict the radio propagation in detail. As a consequence, it isdifficult to predict which base stations need to have a relation andmaybe also a direct connection prior to the network deployment. This wasaddressed in LTE, where UEs could be requested to retrieve uniqueinformation from the system information broadcast of unknown basestations and report to the serving base station. Such information wasused to convey messages to the unknown base station via the corenetwork, which maintained a lookup table from a unique identifier to anestablished S1 connection. One such message was used to requesttransport network layer address information necessary for a direct basestation to base station connection for the X2 interface. For basestation relations in the NX context, a base station is an entity thatterminates the evolved X2 and/or S1 interfaces.

One approach for establishment of such base station relations is viapre-configuration and subsequent removal of unnecessary relations. Theinitial relations can be based on geographical information or logicalinformation such as relations between all base stations within the samecluster interconnected via ‘good’ backhaul. Furthermore, the initialrelations can be very lightweight to enable an extensive set of initialbase station relations. The drawback is that some base station relationsmight not be relevant initially but after some time due to changes inthe environment or in UE mobility patterns. An alternative is toregularly establish extensive base station relations and thensubsequently remove unnecessary relations. For deployment strategy Awith clusters of transmission points within the same base station, it isreasonable that some relations are needed within the cluster for exampleto coordinate system access, but there can still be a need for basestation relations to base stations in different clusters and systemaccess regions.

Therefore, it is concluded that there is a need for an Automatic Basestation Relation (ABR) procedure in NX.

3.9.2.1 Ultra-Lean Broadcast of a Base Station Identifier

The ABR can be based on a similar foundation as ANR in LTE, where a UEis requested to retrieve system information from a different basestation and report back to the serving BS. The procedure is thus basedon broadcast of a base station identifier (BSID). One challenge is tocombine this with an ultra-lean design, specifically relativelyinfrequent broadcast of the BSID compared to the SSI. The periodicity ofthe BSID could be on the same order as the AIT periodicity, and evenassociated to the AIT transmission for both base station and UEefficiency. Note that such infrequent BSID broadcasts most likelycorrespond to worse real time relation establishment performancecompared to LTE, but that is an acceptable degradation, given thebenefits from more ultra-lean transmissions.

Moreover, for efficient UE BSID retrieval, the UE benefits fromknowledge about an approximate search space for BSIDs of non-servingBSs. The first alternative is based on the assumption that base stationsare time aligned on millisecond level, for example via some network timeprotocol, and that BSIDs are transmitted in a network-wide, or at leastregional common search space from a UE perspective. This enables anefficient BSID retrieval also for sparse BSID broadcasts.

The second alternative considers whether base stations are not timealigned, or whether it is desirable to support a more flexible BSIDbroadcast pattern between certain areas. Then, the BSID transmissionpattern can be signaled as part of the AIT, and thereby be tied to thesystem access region. However, such a scheme requires that the UE isable to retrieve the AIT everywhere it is desirable to retrieve theBSID. For example, it can be relevant to broadcast the BSID everywherethe base station is reasonably able to serve connected UEs, whichpossibly could be a wider area than the SSI/AIT covers.

A third alternative is to rely on idle mode UE measurements. UEs can beconfigured to monitor and log SSI, AIT and BSID in addition to thetracking area information, as well as time stamps when in idle mode.Such a log can be provided to a serving base station when the UE hasconnected to the network. The log of transitions between different BSIDscan be used to identify BS relations. Either the serving BS thatobtained the log can retrieve the BSID of an adjacent BS from the mostrecent visited cell, or the serving BS or a central entity like the OAMsystem can use the full log to establish BS relations corresponding toall BS transitions in the log.

A fourth alternative is to rely on radio link reestablishmentprocedures, where the UE provide a new serving base station withinformation about its previous serving base station. It is important toacknowledge that there might be a coverage hole between two basestations that caused the radio link failure. However, the BS relationcan still be very relevant and an important part in an inter-BScoordination to compensate for the coverage hole.

FIG. 141 illustrates some possible BSID information that different UEsmay retrieve from non-serving BS, upon request, to support automatic BSrelations:

-   -   UE1, served by B1, can retrieve the ID of B2 using any of the        four alternatives. It may also be configured to retrieve all        BSIDs that have the same BSID search space configuration as its        serving BS and also be able to retrieve the ID of B2.    -   UE2, served by B3, cannot retrieve any BSID    -   UE3, served by B3, can retrieve the ID of B4 using any of the        first, third and fourth alternative, but not the second        alternative since the SSI/AIT cannot be retrieved in that        location.    -   UE4, served by B3, can retrieve the ID of B4 using any of the        four alternatives.

Moreover, not only the BSID but also the time of retrieval is needed incase the base stations broadcast the BSID in obfuscated mode, meaningthat the BSID is only fixed during a validity time, and the BSID andretrieval time tuple is needed to correctly identify the BS. A signalingchart for the BSID and TNL address retrieval, and automatic X2 setup isprovided by FIG. 142. Steps 1-5 illustrate the retrieval of a uniqueBSID from the PME (section 3.10) or similar despite obfuscation over theair, which is enough to establish a BS relation. In addition, it is alsopossible to automatically retrieve the TNL address information about thenon-serving BS, either via a lookup table in a network node (step 6), orvia a triggered request from the network node to the non-serving BS(step 6 and 7). The retrieved TNL address information can subsequentlybe used to establish an evolved X2 connection between the two BSs.

The transmission of BSID also needs to be evaluated and compared toother means to establish BS relations. One example is based on a centralentity such as the PME coordinating the use of MRSs by the basestations. The base station regularly negotiates with PME which MRSs itcan use. Then BS relations can be established based on MRS reports fromUEs to a serving base station, which are sent to the PME for anassociation to a base station using the reported MRS. Such a solutioncomes at a coordination cost, but it enables a faster BS relationestablishment, in the same order of the LTE establishment times.

3.9.2.2 Base Station Relations Based on Uplink Transmissions

An alternative to ultra-lean broadcast of BSIDs is to let served UEs totransmit in the uplink during a specific uplink search space. In a firstalternative, the information about this BS search space can be validnetwork-wide, and the BSs are assumed to be time aligned on millisecondlevel. This enables efficient BS monitoring of the search space,provided that this search space is sufficiently limited in time andfrequency. The serving BS configures the UE to send an uplink messageincluding the BSID of the serving BS. A non-serving BS that retrievesthe uplink transmission can extract the BSID or at least look it up viaa different node, and thereby establish a BS relation.

An alternative supports non-time aligned BSs, or a more flexibleassignment of the uplink search space between regions. It is based onthat the definition of the BS search space for such uplink transmissionsfrom non-serving UEs is included in the AIT or similar, and is thereforeconfigured as part of the system access. This requires that the UEretrieves the SSI/AIT of the non-serving BS and reports to its servingBS.

Note that since the BSID in this case is not broadcasted by the nodes,the need for obfuscation is not as strong. Possibly, the uplinktransmission could be obfuscated to be on the safe side. Signaling withsome different options is illustrated by FIG. 143, which is a signalingchart for uplink-based ABR. Steps 1-2 are only needed if the uplinksearch space is defined by the SSI/AIT. Also, steps 5a and b are onlyneeded if the BS needs to lookup the UBSID from PME based on theretrieved ULID and time. Again, steps 3-5 (1-2 optionally) are needed toestablish a BS relation, while steps 6 and optionally 7 are needed torecover the TNL address and make the relation mutual, while steps 8-9are needed to automatically establish an evolved X2 connection.

3.9.3 Beam Relations Establishment

When BS relations have been established, base stations can interact tocoordinate and inform about transmissions. One possible use of suchinteractions is to establish relations between mobility beams ofdifferent base stations and nodes/transmission point associated to thebase stations as discussed in section 3.5. Some important aspects whendiscussing relations between beams:

-   -   the relations should not be related to transmitted MRSs        explicitly associated to beams to avoid an MRS planning problem.    -   the nodes should be able to benefit from altering beams by        tuning beams, splitting beams, etc.    -   the relation could also be based on the uplink time alignment        value to further narrow down the candidate beams for the        handover of the UE.    -   the relation table supporting handover from a beam of the source        node to a beam of the target node could reside in the source        node or in the target node.

The relations between beams in NX can therefore be something differentthan the relations between cells in LTE.

In order to address the first two aspects, the notion of virtualmobility beams is introduced. A virtual beam of a node N is representedby an index i, i=1 . . . , M. In the sequel, the virtual beam i of nodeN is denoted VBNi, e.g., VB21. The considered procedure to automaticallycreate mobility beam relations is therefore denoted Automatic Virtualbeam Relations (AVR) to emphasize that the relations are between virtualbeams. To support mobility, a node can realize a virtual mobility beamby one or more transmitted mobility beams, each assigned an MRS. Theassignment of MRS to a mobility beam is not fixed and typically variesfrom one time window to the next. The virtual beam concept can alsoaccommodate and support uplink based mobility, where a virtual beam canbe associated to uplink reception, possibly with directivity. Thediscussion below is based on downlink based mobility, but the discussionmore or less applies to uplink based mobility as well.

FIG. 144 provides some more insights into virtual beams and virtual beamrelations, from the perspective of the virtual beam VB21 of node B2. Ithas one virtual beam relation to VB11 of node B1 and another to VB31 ofnode B3. The virtual beam VB11 is realized by a mobility beam assignedto MRS M1 and VB21 is realized by a mobility beam assigned to MRS M2.Furthermore, the virtual beam VB31 is realized by two mobility beamsassigned to MRS M3 and M4 respectively. It is also reasonable to try toassociate a served UE to a serving virtual mobility beam, either viadirect measurements of periodically transmitted mobility beams from theserving node, or by associating the serving downlink or uplink beam(typically UE-specifically tuned) of the UE to a virtual mobility beam.

When node B2 triggers the need for mobility measurements on behalf ofthe depicted UE, the node takes advantage of the virtual beam relationsbetween VB21 on one hand and VB11 and VB31 on the other. In this case,the realized mobility beam configured with MRS M3 is the most favorablealternative.

The virtual mobility beam relations can also be refined to be separatein the uplink and downlink, and may also consider the uplink timealignment to the serving node. In the following, uplink and downlinkrelations are assumed to be the same, and the serving node is the samein uplink and downlink, which means that the uplink time alignment isapplicable also to the serving downlink beam. (In case or uplink anddownlink split, the uplink time alignment reflects another node than theserving downlink node, which means that the uplink time alignment cannotbe associated to the serving downlink beam.)

The uplink time alignment is put into the context of virtual mobilitybeam relations in FIG. 145. Here, the relations are not only betweenvirtual mobility beams, but also including a TA range associated to theserving node. The virtual mobility beam VB21 now has one virtual beamrelation from TA range TA1 to VB11 of node B1 and another from TA rangeTA2 to VB31 of node B3. When node B2 triggers the need for mobilitymeasurements on behalf of the depicted UE with a TA within the TA rangeTA2, the node takes advantage of the virtual beam relations betweenVB21, TA2 on one hand and VB31 on the other. Thereby, only node B3 isasked to transmit mobility beams which are associated to virtualmobility beam VB31. Also in this case, the realized mobility beamconfigured with MRS M3 is the most favorable alternative. The TA rangesmentioned above are established from TA statistics based on successfulhandovers and will be improved over time with more statistics.

The concept of virtual mobility beams and virtual mobility beamrelations means that the virtual mobility beam can be a mobility beamwith any MRS, and is an alternative to a fixed association between beamand MRS which brings an MRS planning problem. A design based on avirtual mobility beam concept implies that an association between thelogical virtual mobility beam and the realized mobility beam with itsassigned MRS needs to be communicated to other nodes together withinformation about allocated resources via the evolved X2 or S1. Thereby,UEs can be informed about which search spaces the UE shall considerand/or which MRSs to search for. The design also ensures that anypossible MRS collision from two different nodes can be predictedbeforehand. Since the MRS to mobility beam allocation is not fixed insuch a design, this enables obfuscated operation of mobility beams.

The virtual mobility beam relation table considered for a handover froma source node to a target node can reside in the source node or thetarget node. These are synchronized between target and source nodes,since the beam relation tables are needed for handover in bothdirections between two different nodes.

The relations between virtual mobility beams are established based on UEobservations and reports. These observations are made when associatedmobility beams are transmitted. Depending on the situation, thetransmitted mobility beams can be initiated differently. Two situationsare considered in the following two subsections. Moreover, establishingvirtual mobility beam relations from RLF events is addressed in thesubsequent subsection. A fourth alternative is where positioninformation is available from GNSS or some other non-NX based system,which are addressed in the last subsection of virtual mobility beamrelations section.

3.9.3.1 Establishment of a Green Field Network

When all nodes in an area are deployed at the same time, there areplenty of virtual mobility beam relations to establish, and the trafficis typically relatively low. Therefore, in order to establish therelations quickly, it is relevant to use the available UEs as much aspossible for extensive observations. The green field deployment benefitsfrom a dedicated training procedure, which is agreed upon once the basestation relations have been established.

As illustrated by FIG. 146, which illustrates virtual mobility beamrelation establishment for green field deployments, once the basestation relations have been established, the base stations agree on acoordinated virtual mobility beam relation measurement phase. In theconfiguration, the base stations may coordinate the use of MRSs to avoidcollisions, and to maximize the number of observations within a limitedtime. The configured MRSs are associated to virtual mobility beams aswell as mobility beam realizations by each base station. Optionally, thevirtual mobility beam relations are associated to the uplink timealignment and specifically different TA ranges.

3.9.3.2 Establishment of a New Node in a Mature Network

When a new node is established in a mature network, there is typicallyalready a large amount of served UEs that trigger handover procedures.Every such handover procedure triggers transmissions of mobility beamsconfigured with MRSs. It can therefore make sense to try to utilizethese mobility beams for measurements by UEs served by the new node.This can be made in different ways:

-   -   The new node requests mobility beam information for all        transmitted mobility beams from neighboring base stations.        Whenever a base station initiates a mobility beam, it notifies        the new node in time to allow that node to configure its served        UEs for measurements.    -   The new node requests additional mobility beam transmissions        from neighbor base stations, and to be informed when these are        transmitted.

Both these are illustrated by FIG. 147, which illustrates virtualmobility beam relation establishment for mature deployments, with theoptional step 2 addressing the request from the new base station toanother base station to transmit excessive mobility beams. Step 1concerns the request for mobility beam information to enable learningfrom mobility beams transmitted to support handover between existingbase stations and transmission points. At the same time, the new BStransmits mobility beams for served UEs to measure on as well. In asimilar manner, information about these mobility beams from the new basestation to the neighboring base stations.

3.9.3.3 Virtual Mobility Beam Relations from RLF Reports

Inappropriate virtual mobility beam relations may lead to radio linkfailure (RLF) when the serving node cannot maintain the connection tothe UE. Since the UE has an established context in the network, the UEdoes not initiate a completely new connection but tries to re-establisha connection to the network, typically towards a new/target basestation. This can also be seen as a procedure to establish the requiredrelations without any additional information broadcast from thenodes—though some of the initial UEs experience radio link failure, theprocedure learns the required beam relations from such failures andbecomes more robust in the future.

The steps 1-7 of FIG. 148 address the connection re-establishment aswell as establishment of a virtual mobility beam relation, based on RLFreports:

-   -   1. The UE is informed about the BSID of the serving BS as part        of some connection configuration procedure.    -   2. The UE is regularly associated to a virtual mobility beam,        either via UE or BS measurements, or relating a serving data        beam to the most appropriate virtual mobility beam.    -   3. The radio link of the UE fails. The source BS maintains the        UE context.    -   4. The UE saves measurements, states and time of failure.    -   5. The UE re-establishes with the target BS or node, and        provides UE ID and BSID at source BS to the target BS. The        target BS either has been provided with the UE context already        if handover has been initiated, or can retrieve the UE context        from the source BS using the UEID and BSID. The UE context may        include an association to a virtual mobility beam.    -   6. The target BS associates the UE to a virtual mobility beam in        the target BS.    -   7. The target establishes a virtual mobility beam relation        between the associated virtual mobility beams at source before        the RLF, and at the target after the RLF (here, the source node        is assumed to keep the UE context until receiving the        re-establishment information for the UE after experiencing RLF        for the UE). Optionally, the source TA is retrieved from the UE        context and included in the relation, and/or the target TA is        established and included in the relation.

Provided that the re-establishment procedure is reliable and prompt,then it can be seen as an adequate means for establishing virtualmobility beam relations. Maybe some RLFs can be considered a reasonableprice compared to the limited overhead, but the associated performanceneeds to be related to customer requirements.

As the UE can be agnostic to the serving beam ID and/or serving BSID,the UE re-establishment procedure can be initiated by the source basestation informing potential target base stations, as illustrated by FIG.149, which shows a re-establishment procedure initiated by source BSwith enhancements to virtual mobility beam relations. Based on theamount of information available to the UE at the moment of RLF,different amount of additional information might be exchanged betweenthe original source BS and the re-establishment BS.

If the UE is agnostic to the serving BS and to the serving beam, thenthe serving BS needs to send notification to its neighbors about the UE,as shown in FIG. 149. By voluntarily acting to send the UE's RLF noticeto the neighboring base stations, the serving base station opens up forfuture signaling from the re-establishment node. Note that the step-2 inFIG. 149 could be replaced with the UE notifying the re-establishmentnode about the previous serving node if the UE is only serving-beamagnostic rather than both serving-beam and serving-node agnostic.

In the step-4 of FIG. 149, information is exchanged not only about theUE's context but also information that aids in enhancing the virtualmobility beam relations. The re-establishment BS informs the originalserving BS about the current virtual mobility beam that is beingassociated to the UE based on which the serving node can update itsvirtual mobility beam relations. Also the source node can re-evaluatethe active mode procedure triggering thresholds in the UE's originalserving beam configurations

3.9.3.4 Position Information and Virtual Mobility Beam Relations

If a base station and UE are capable of regularly, or in an on-demandfashion, establishing a UE position estimate, then the virtual mobilitybeam relations can be based on the position information. This is alsorelated to the considered positioning mechanisms and the associatedpositioning architecture. One advantage is that the source BS does notneed to associate the UE to a virtual mobility beam at the source BS. Onthe other hand, the combination of an associated virtual mobility beamat the source BS as well as an uplink time alignment can in combinationbe seen as a coarse position estimate, and therefore the positioninformation based virtual mobility beam relations can be seen as thesame as discussed above. However, if the position information isindependent from the mobility beams of the source BS, then the positionto virtual mobility beam relations can be seen as a crowd sourcing ofvirtual mobility beam relations.

Building of such a table involves gradual learning, either via machinelearning techniques or via SON research approaches or both, as toidentify which radio feature best represents the position of the UE(when the geo-position of the UE is not available directly), relatingthe accuracy of the geo-location to the virtual mobility beams, as wellas the associated mobility beams and continuously optimizing thecontents of the table to suit the network changes (changes in theinfrastructure of the city, changes in the deployment etc.). Theposition accuracy also has an impact on the reasonable size of thevirtual mobility beams.

3.9.4 Mobility Robustness Optimization

The mobility procedure is explained in section 3.5. The explainedbeam-based procedure requires a self-organizing functionality in orderto reduce the overhead of the MRS transmissions without a significantimpact on the mobility robustness of the beam switch procedure. The SONfeatures mentioned below assume the presence of base station relationsand virtual mobility beam relations, as mentioned in sections 3.9.2 and3.9.3. Also, a SON function similar to CIO (Cell Individual Offset)threshold tuning carried out in LTE but at the beam level ispossible—the beam individual offset (BIO) tuning complements its LTEcounterpart.

3.9.4.1 Handover Procedure Tuning Based on Virtual Mobility BeamsRelation Tables

The virtual mobility beam relations support the handover procedure topropose suitable virtual mobility beams. The serving node determineswhich virtual mobility beams (and associated mobility beams withconfigured MRSs) needs to be transmitted from itself and also eitherrequests the neighboring nodes to transmit specific virtual mobilitybeams or informs the neighbors about the associated virtual mobilitybeam at source, which the neighbor uses to determine the related virtualmobility beams in the target node. The source and target BS uses thevirtual mobility beams to generate associated mobility beams. Forexample, the virtual mobility beam can be associated to one or moremobility beams as illustrated by FIG. 144.The association betweenvirtual mobility beams and mobility beams, as well as the mobility beamconfiguration itself, can be adapted over time.

Under the assumption that the AVR SON function is running for longenough duration to build a virtual mobility beam relation table withsufficient confidence, the HO procedure can be further refined to makeit faster. A HO border scenario is shown in FIG. 150. The virtualmobility beam relation for a UE at the square is associated to onemobility beam A3 at the source node A and one mobility beam B2 at targetnode B. Since the UE is only requested to measure on only one targetmobility beam, then a blind handover can be considered instead withoutconfiguring the UE to measure and report mobility beams. Therefore, allthe steps until ‘Network Preparation’ stage in FIG. 106 could beavoided, to speed-up the HO procedure.

3.9.4.2 Dynamic Geo-Fence Management

The concept of geo-fence is mentioned in section 3.5.2. Just tosummarize the concept of geo-fence again, it is the active mode UEcoverage identifier for the node. Such a geo-fence could be used forpro-active (without waiting for the SINR to drop below certainthreshold) triggering of the active mode handover procedure. A geo-fenceis created with the help of a geo-fence beam (geo-fence beam is a MRSbeam wider than the narrow MRS beam and this beam is transmittedperiodically from the node when at least one active mode UE is connectedto the node) and some relative thresholds in each narrow MRS beamdirections. This method is further illustrated with the help of FIG.151. In the figure, the narrow MRS beams are identified, and thegeo-fence area is the shaded area overlapping the narrow MRS beams. Inthis method, the geo-fence area is generated with the help of ageo-fence beam, in that there is a physical beam transmitted from thenode to create the shaded area in FIG. 151. The geo-fence area for sucha geo-fence beam is defined with the help of thresholds in each of thenarrow MRS beam. Therefore, when the UE is in narrow MRS beam-1 then thethreshold-1 is used to identify the coverage of the geo-fence beam andwhen the UE is in narrow MRS beam-2 then the threshold-2 is used toidentify the coverage of the geo-fence beam and so on. In this way, a UEin the narrow MRS beam 1 uses threshold-1 as a relative offset towardsthe signal quality of the geo-fence beam to trigger an event triggeredmeasurement report.

In the initial deployment stages of the node, based on the drive testmeasurements or any other available pre-knowledge, OAM can identify thegeo-fence for a give node and it can configure the node withcorresponding geo-fence related thresholds directly. As one would preferto reduce the drive tests, one could see this as a non-drive test basedconfiguration, wherein the OAM configures each of the thresholdscorresponding to the narrow MRS beams to the same value and lets thegeo-fence management SON function optimize these thresholds.

A geo-fence can be further optimized based on different measurementscollected by the node from the UEs and the performance of HO decisions.The shape of the geo-fence depends on the tuning of the beam relationparameters based on not only the performance of the HOs in the past, butalso the node capabilities involved in the HO borders. As an example,the geo-fence beam's shape can differ significantly in certain narrowbeam directions compared to other narrow beam directions. This isillustrated in FIG. 151. As shown in the figure, the coverage of thegeo-fence beam can be limited via different thresholds in differentdirections based on the narrow MRS beams' quality and the performance ofthe neighboring node beam's (not shown in the figure but the currentnode is assumed to have neighbors) qualities. Also note that even thoughthe signal strength measurements of the geo-fence beam of a particularnode is better than the signal strength measurements of the geo-fencebeam of another node at a particular position, it does not guaranteethat the position belongs to the first node in terms of first node'sgeo-fence region, as the node capabilities in creating the narrow beamsdictate how large or small the geo-fence of a node is.

Therefore, a dynamic geo-fence management SON function optimizes theactive mode mobility procedure triggering location based on the HOstatistics (Ping-Pong behaviors between the nodes, handover failuresetc.), node (self and neighbor) capabilities and also possibly on loadsituations. The controlled parameter is the threshold value that isspecific to a narrow MRS beam.

3.9.5 Self-Optimization and Healing

Several SON functions such as identity management, entity specificparameters, load management, coverage and capacity optimization,cognition and self-healing, are briefly commented upon in this section.

3.9.5.1 Identity Management

When operating the network in obfuscated mode, the ambition is toregularly change transmitted sequences and identifiers. This can also beseen as a way to avoid the planning problem of identifier assignment forlocal uniqueness. The identifiers mainly reside in the network andbetween network elements, and the transmitted identifiers and sequencesare regularly changed in coordination with a PME.

3.9.5.2 Entity Specific Parameters

Detailed procedures of the network elements may be subject toautomation, provided that there are systematic aspects such as radioconditions to adapt.

3.9.5.3 Enhanced Load Sharing Between Neighboring Nodes

A beam can potentially serve the UE with a good channel quality evenwhen the UE is outside the geo-fence of a node. This is highly likely tobe the case when the neighboring node is not interfering, e.g., due tolack of activity in the beam/s towards the UE. Though the neighbor isnot transmitting any beams in the direction of the current UE, theneighbor could be overloaded due to high activity in other beams. Thishas an impact on the backhaul and other processing overhead in theneighbor. One example of a mobility load balancing scenario is shown inFIG. 152.

In FIG. 152, the UE moves from node A towards node B and once the UEgoes outside the coverage of node A, then in the geo-fence based HOtriggering method, the HO procedure is triggered towards node B. Basedon the MRS measurement results, the node A recognizes that the HOcandidate is node B and specifically beam B2 in node B. When the node Arequests for the HO to beam B2 the node B can defer from accepting theHO if it realizes that the node A can serve the UE sufficiently well.(Note that node B is serving several other UEs in different beams whichmight cause more processing overhead and backhaul overhead in node B.)In such a load balancing feature, the node B can further only getcertain measurements from the node A related to the UE to make sure thatthe UE is not suffering because of the in-efficient beam quality fromnode A.

3.9.5.4 Coverage and Capacity Optimization

With a beam-based system, the ambition is to always provide an adequatebeam to the UE. At the same time, the network and service coverageshould be maintained and predictable. Therefore, it is important tore-evaluate the coverage and capacity situation in the network to assesswhether deployments of additional network elements are needed, or if theexisting can be reconfigured to accommodate the needs of the users.

3.9.5.5 Cognition and Self-Healing

Much of the assessments and analysis today take advantage of theextensive broadcast of reference signals and identifiers. With morerestricted transmission of such identifiers, it is important to stillsupport root case and analytics use cases properly.

3.10 Positioning

Positioning in NX aims at addressing vastly different positioning needsand differentiation between users, device types, services etc. Signalsand procedures for positioning in NX are flexible, to meet therequirements.

3.10.1 Requirements and Capabilities

With a multitude of potential applications and use cases, therequirements can be stated along multiple dimensions, as exemplified andillustrated by FIG. 153, which illustrates positioning requirementstrade-offs, illustrated by a critical application (shaded area extendinggenerally horizontally) such as an emergency call or autonomous vesselassociated to a device, and a non-critical application (shaded areaextending generally vertically) such as sensing or network management.The set of requirements is thus more heterogeneous than only accuracyrequirements.

Physical Layer Requirements:

-   -   Cost concerns CAPEX and OPEX costs of the operator associated to        positioning, as well as radio resources allocated to positioning    -   Energy efficiency aspects can be relevant at both the network        side and the device side and concerns to what extent energy        efficiency is a consideration or not. Also related to costs.    -   Accuracy requirements range from crude (100 m) to very accurate        (submeter). A related requirement is regarding accuracy        assessments, which implies that the estimated accuracy of an        estimated position should be stated.

Protocol Oriented Requirements:

-   -   Protocol aspects concerns whether the positioning is supported        by a very specific protocol such as the LTE Positioning protocol        between a UE and a network node, or if it is a mix of different        protocols including user plane and control plane signaling,        access and non-access stratum signaling etc    -   Device type dependency concerns support for various limitations        associated to devices and tags.    -   State dependency is a requirement that dictates whether the        device can be positioned in different states such as        idle/dormant/active

Architecture and Deployment Requirements

-   -   Deployment relates to whether positioning poses requirements        that affect and influence the deployment configuration.    -   Absolute/relative position requirements with estimates either        related to a known geographical reference, or only to a logical        entity, maybe with uncertain or even unknown position.    -   Time to fix, the time from when the positioning request is made,        to when the position estimate is provided to the requester, can        be of different importance and at different level depending on        application. For example, vessel autonomy would have stricter        requirements than an emergency call.    -   Flexibility to support different requirements over time    -   Scalability to support applications with vast number of devices    -   Network architecture aspects are also related to time to fix and        scalability, as well as the network slicing aspects. Some        applications may require that a specific network node is        involved, while others are fine with support from a logical        network function that can be virtualized anywhere.

Higher Layer Requirements

-   -   Differentiation concerns the ability to simultaneously provide        different grade of positioning performance to different        applications, devices, services, etc    -   Privacy dictates whether positioning information should be        anonymized for the operator, and whether the network supports        anonymized UE-based positioning.    -   Security concerns whether a third party can retrieve some        positioning information

FIG. 153 illustrates the requirements by two example use cases. Thefirst use case represents a critical application where strict time tofix, accuracy, security, protocol aspects and state dependencyrequirements are most important and scalability is less strict. Thesecond use case illustrates a non-critical application for sensing andnetwork management where instead strict flexibility, scalability, costand privacy requirements are most important, and requirements onaccuracy, state dependency and protocol aspects are less strict.

The scope of positioning opportunities is also very much dependent onthe capabilities of the terminal. FIG. 154 lists some typicalcapabilities, and some examples of different level of device complexity.Different device complexities can for example be associated to supportof different numerology, where simple devices are limited in terms ofsupported bandwidth and symbol time etc. The device complexity can alsobe associated to how the device is powered, which is closely related toenergy efficiency aspects. Some devices are pre-configured and cannot bere-configured once deployed, while others are capable of retrieving somecommon information, and even more capable devices can retrieve dedicatedconfiguration information.

Devices can also have different capabilities when it comes to support ofdifferently complex downlink reception and uplink transmission schemes.Simple devices may be configured to only transmit in the uplink, whileslightly more complex devices can measure and report downlinkmeasurements. Beam forming and codebook-based may require an even moreadvanced device etc. Also, some devices are capable to taking advantageof their own position, while simpler devices only enable some other nodeto determine its position and use in applications.

3.10.2 Common and Dedicated Functions

NX positioning components can be configured as common or dedicatedcomponents to enable both scalable and crude positioning as well asaccurate and tailored positioning. Common Positioning Reference Signals(PRSs) and contention-based uplink signals can be configured via aspecific Positioning Information Table (PIT) or some other table such asAccess Information Table (AIT). Dedicated components include dedicatedPRSs, dedicated Uplink Synchronization Signals (USSs), and dedicatedprocedures. A positioning procedure may be initiated via commonprocedure to be refined via dedicated procedures. The geographicalassociation to a component can be included in assistance data to the UE(UE-based positioning), or be configured in a database in a networknode, where the association is made based on UE feedback (UE-assistedpositioning). Both positioning strategies are supported in previousgenerations, and are supported also in NX.

3.10.2.1 Common PRSs

Some common signals can be seen as instances of PRSs, such as the SystemSignature (SS). In addition, there can be additional common PRSs definedand the UE has to retrieve information about such PRSs via scheduledsignaling in active mode. The configuration information is denoted thePositioning Information Table (PIT), which may be associated to avalidity region characterized by a SSI or a tracking area. It is up tothe UE to monitor the validity of the PIT and retrieve an update oncethe region has changed. This means that common PRSs can be monitored inessentially any state.

A common PRS may be node specific, or common for a set of nodes. It mayalso be beam specific. The common PRS may also be transmitted via adifferent RAT such as the existing PRSs of LTE.

3.10.2.2 Common Contention-Based Uplink Signals

Common uplink signals such as PRACH preambles can be used to establishuplink time synchronization at a node. Since the signals are common,contention has to be handled to ensure the true identity of the device.The configuration information about these common signals can be providedto the UE via broadcast information or scheduled information

3.10.2.3 Dedicated PRSs

The PRSs can also be configured in a dedicated fashion, either to extendthe common PRSs to enhance performance or to refine the resolution ofPRSs in time and/or space. One typical PRS configuration is the TimeSynchronization Signal (TSS) for timing estimation, typically incombination with a Mobility Reference Signal (MRS) to refine timingestimation and enable beam identification. A PRS is a configurationtowards a UE, which means that given a transmitted TSS, one UE can beconfigured to use the TSS for timing estimation, while another UE isconfigured to consider the TSS as a realization of a PRS.

Furthermore, dedicated PRSs can also be configured by extending TSS andor MRS in time and/or frequency. In one example, a node is configured totransmit identical sequences for TSS and MRS in two consecutive symbols.One UE is configured to utilize the transmission of the first symbol asa TSS/MRS, while another UE is configured to use the sequences of thetwo symbols as a PRS.

3.10.2.4 Dedicated Uplink Synchronization Signals (USS)

Time alignment during random access aims at aligning the time withrespect to a node. The UE is assigned an USS to enable uplink timingestimation. The procedure can also be seen as a round-trip timeestimation procedure, which potentially can use the USS as is or berefined by an enhanced USS with even better support for timingestimation.

Furthermore, multiple nodes may receive the USSs to enable uplink TimeDifference of Arrival (TDOA). To support such positioning, theinformation about the USS needs to be signaled between nodes, or atleast to the corresponding baseband processing unit.

3.10.2.5 Combining Common and Dedicated Components

FIG. 155 exemplifies some common and dedicated components, where thecommon components are defined in a validity region characterized by theSSI area. Positioning can be gradually refined from crude and supportedby the common PRS transmitted by a set of nodes, to accurate andsupported by some beam-specific dedicated PRSs. The UE needs to retrieveinformation about the dedicated PRSs in UE NX active state. Onceretrieved, measurements can be aggregated and processed in any state(active, dormant, idle).

3.10.2.6 Network Synchronization Challenges

Some positioning frameworks such as uplink and downlink time differenceof arrival are based on information about the relative timing betweennodes or the corresponding baseband units. For crude positioning, thenetwork synchronization is less of an issue, and the current networksynchronization procedure based on Global Navigation Satellite Systems(GNSS) suffices. It implies a timing error standard deviation in theorder of 50 ns [3GPP37.857] corresponding to 15 meters. However, forsub-meter accuracy requirements, this is not accurate enough. Therefore,clock synchronization based on over the air measurements is desirable.An alternative is to use mechanisms that utilize ranging and directionmeasurements, which in combination can provide accurate positioningwithout accurate inter-node synchronization.

3.10.3 Restricted Availability of Positioning Information

There can be several reasons to restrict the availability of positioninginformation. One is that regular transmission of PRSs has an impact onenergy consumption of a node since it limits node sleep. If there are noUEs taking advantage of the PRSs, then their transmission should beavoided. Moreover, if such signals are semi-statically configured, then3^(rd)-party applications can be used to register the PRSs, associatethem to geographical positions and store the data in a database. Thisdatabase then enables 3^(rd) party applications to measure PRSs andcorrelate with the established database to enable positioning of thedevice. An operator might be interested in restricting the access toPRSs to only its customers, possibly with some differentiation.Restricted availability of and access to positioning information is anew concept for NX and is therefore described in more detail than thePRS components in the previous subsection.

In general, a PRS can be seen as sequences/resources/descrambling thatare functions of time (t) and, frequency (f), node ID (id₁), system ID(id₂) PRS ID (id_(PRS)), etc that can be semi-statically configured. Byadding a time-varying parameter a(t) that is altered regularly and hasto be retrieved via dedicated signaling:

PRS_(n) =f(id_(n), . . . , α(t))

It is possible to define a PRS with a validity time or access time inthe sense that a UE needs to retrieve information about α(t) once itscurrent information has become outdated. Thereby, it is not possible torecord PRSs via over the top applications since this information is onlyvalid for a limited time.

This is exemplified in FIG. 156, where different nodes transmitdifferent positioning reference signals. The signals are not fullyuseful for the UE unless it knows the time varying sequence α(t) used togenerate the signals. In this example the time-varying parameter α(t) isdenoted a “positioning key” since it enables the UE to unlock the highaccuracy positioning capabilities provided by the network.

Example signaling is provided in FIG. 157. In this example, a networkentity denoted Positioning management entity (PME) configures thenetwork nodes with a time-varying dedicated PRS configuration. Thenetwork node n transmits a dedicated PRS_(n) (on behalf of some otherUE, probably) that is a function of the time varying PRS configuration.Since the UE in this example has no information about the currentdedicated PRS configuration, it cannot perform a high accuracypositioning using the dedicated PRS signals. Optionally it may perform alow accuracy positioning e.g., using common PRS information that is nottime-varying.

If the UE determines that it wants to perform a high accuracypositioning using dedicated PRS signals it sends a request to thenetwork (typically via the currently serving node that may then forwardsthe request to the PME node) and receives in response the informationrequired to perform high accuracy positioning.

After some time, the current positioning expires and the PME configuresthe network nodes with a new dedicated PRS configuration (or itsreconfiguration pattern might be configured for a longer period oftime). Unless the UE has received an update containing informationrelated to this new configuration it can now no longer perform a highaccuracy positioning.

Note that the example provided in FIG. 157 is just an example.Alternative solutions could be that the network nodes handles the PRSexpiration timers and re-configuration autonomously, after an initialconfiguration, e.g., by an OSS (operation and support system) or SON(self-optimizing network) node.

Differentiated positioning accuracy can be enabled in many differentways e.g., by one or more of:

-   -   Providing a positioning key that is valid for a short time or        for long time duration.    -   Providing information that enables the user terminal to decode        only a selected sub-set of the available PRS signals transmitted        from the network.    -   Making selected parts of the PRSs decodable to the UE (e.g., in        time and/or bandwidth).    -   Providing additional PRSs in response to a higher accuracy        request.

3.10.4 Flexible Reference Nodes

In previous generations, the positioning infrastructure has been networknodes such as base stations, transmission points, etc. However, in someuse cases, the density and geometry of network nodes are insufficient toprovide accurate positioning. Furthermore, some applications and usecases rely on relative positioning between entities, and accuraterelative positions are more important that absolute positions. Oneexample is use cases with autonomous vessels with humans in thevicinity. In such cases, the relative position is vital to avoidaccidents.

Therefore, it is relevant to consider some devices to be part of thepositioning infrastructure.

In order to be clear, the following distinction is made:

-   -   Positioning—determination of the whereabouts of a device, which        can be estimated based on signals from infrastructure nodes and        devices.    -   Location—whereabouts of a piece of infrastructure, which can be        either network nodes or other devices. Note that the location of        such a device can be determined via positioning.

Devices that support positioning may either have specific capabilitiessuch as a capability of self-positioning in absolute terms (e.g., GNSS)or in relative terms (e.g., radar, sensors). These devices are referredto here as positioning support devices. These devices at least have thecapability of transmitting a positioning reference signal, or even thecapability of supporting a ranging and/or bearing estimation procedure.

FIG. 158 illustrates a signaling example with device 1 that acts as apositioning support device and thereby enhances the positioning of adevice 2. The positioning support device informs the network node aboutits capability, and receives a PRS configuration. One example of a PRSis the sidelink discovery signal in LTE, enhanced with a reportingprocedure.

3.10.5 Ranging Procedures

The purpose of uplink timing alignment is to establish an uplink timingthat is approximately equal for all served UEs at the same node. It istypically established during random access and maintained during theduration of the connection based on feedback from the node to the UEwith relative timing adjustments.

Ranging can also be an important component in positioning, but itrequires range estimates from at least two to four nodes depending onwhether a time series of measurements is available, and whether a 2D or3D position is required. Therefore, it can be relevant to design aranging procedure towards non-serving nodes. It is natural to base sucha procedure on uplink time alignment which starts from random access.Hence, the UE needs to be authorized and configured to be able toinitiate random access to a non-serving node. The configuration can bevia one or more of

-   -   the AIT providing system access information, where optionally        some random access preambles may be restricted for access of        non-serving devices.    -   the serving node, providing information about random access        procedures to non-serving nodes, including both random access        preambles as well as related downlink reference signals.    -   pre-configuration, where a specific downlink reference signal        indicates acceptance of the reception of a random access        preamble for non-serving ranging.

The UE initiates the ranging by monitoring a downlink reference signal(a PRS or some other DL RS) associated to non-serving node ranging.Based on the received timing of the downlink signal, or an uplink timingrelated to the serving cell, the UE transmits a random access preambleto the non-serving node, and awaits a response in a pre-configured orconfigured time/frequency resource or search space. The response mayinclude an initial uplink timing, and may include an uplink resource andtransmission configuration for subsequent uplink transmission. Thetransmission/response procedure may continue until a satisfactoryranging accuracy has been achieved. The procedure may compriseconfiguration of gradually wider uplink and downlink signals to enablegradual accuracy improvements.

3.10.6 Direction Estimation Procedure

The serving node interactions may include feedback about the favorablebeam or beams, typically associated to an MRS. The feedback may alsoinclude the received signal strength of the MRS. The node can therebyassociate to the UE a direction estimate based on the direction andwidth of the favorable beam. A prerequisite is that the beam has beencalibrated to a spatial direction. Such calibration can be performed bygathering some accurate positions in a training phase via GNSS orsimilar, and associating such positions to favorable beams.

One way to refine the direction estimates is to not only request the UEto report the favorable beam but to configure multiple beams in thedirection where the UE approximately roams, and request the UE to reportthe received signal strength from multiple beams. The feedback can beefficient if considering relative signal strength reports as thereceived signal strength relative to the strength of the favorable beam.

If the beams stem from the same node, and the radio propagationconditions can be considered to be the same, then the relative signalstrength between two beams is equivalent to the relative antenna beamgain between the beams. With calibrated beams, this can be translatedinto very accurate direction estimates.

3.11 Device-to-Device Communication

While a first set of LTE D2D features were first added in Release 12, NXincludes D2D capabilities as an integral part of the system. Thisincludes peer-to-peer user-data communication directly between devicesbut also, for example, the use of mobile devices as relays to extendnetwork coverage.

3.11.1 Basic Rationale and Desired Features for D2D Communications

In LTE, a rudimentary support for D2D communications was first added inRelease-12. The main functionalities were developed for the publicsafety (PS) use case, including intra- and intercell (in-coverage),outside network coverage and partial network coverage scenarios. Fornon-public safety use cases only discovery within network coverage wassupported. For Release-13 and Release-14 the scope of D2D communicationswill be extended both for PS and commercial use cases, including supportfor V2X communications. Still, the currently supported LTE D2Dcommunications technology components are not designed to fully harvestthe potential of the coverage, capacity and delay gains that D2Dcommunications are expected to deliver.

For NX, D2D communications capabilities are supported as an inherentpart of the system rather than as an “add-on” feature. The basicrationale for D2D communications as a technology component is that D2Dtransmission should be used whenever it is (1) more efficient in termsof spectral efficiency, energy efficiency, achievable latency orreliability or (2) can provide a better service experience thantraditional cellular communication.

The D2D features that are or will be supported by Release-12, -13, -14D2D are also supported by the NX D2D design. In addition, the NX D2Ddesign supports additional features that are motivated by new use cases,requirements or performance enhancements. To summarize the D2D scenariosand to establish some basic D2D related requirement list, the D2Dscenarios are summarized in FIG. 159. These scenarios may be helpful toidentify desirable features and design options, but D2D technologycomponents under discussion are not and should not be tightly connectedto or limited by these scenarios.

FIG. 160 lists desirable features related to D2D and compares theircurrent status with how that requirement applies to NX. Unicast(point-to-point) D2D communication can be seen as a base case, that—whenmode selection, resource allocation and power control are properlyapplied—can much improve the network performance when proximalcommunication opportunities exist. Multicast and broadcast communicationby means of D2D is supported from 3GPP Rel-12. In NX, there can beperformance enhancements to support a longer multicast/broadcast rangeand higher rates without affecting the cellular layer. Support for D2Dbased relaying in partial network coverage situations exists already inRel-12, but the performance both in terms of range extension andachieved end-to-end rates can be expected to increase by appropriaterelaying device selection and RRM functions.

Cooperative communications enabled by network controlled and assistedD2D communications can take many different forms at various layers ofthe protocol stack, such as distributed device based content caching anddistribution, cooperative MAC protocols and, for example, network codingenhanced cooperative relaying. Likewise, some forms of D2D communicationoutside NW coverage is supported already in Rel-12 (e.g.,multicast/broadcast), but in NX D2D is further developed to cover largerareas in, for example, disaster situations and provide higher bit rateservices even in (temporarily) out-of-coverage areas.

3.11.2 NX Design Principles and D2D

TABLE 17 NX design principles and their applications to D2D in NX NXdesign principles Implications on D2D design in NX Use ultra-leantransmission Already that way compared to traditional cellular,possibility on R12/13 SLSS (side-link sync signal) reduction comparedwith Rel-12. Use self-contained Already that way compared totransmissions traditional cellular, possibility on integrated controlchannel and data channel Avoid strict timing relations Take advantage ofUL/DL flexibility (no across subframes explicit restriction to constrainD2D to uplink resource/(either carrier for FDD or subframe for TDD))Avoid slow reconfiguration To enhance control plane reliability and ofdynamically changing flexibility (to support multi-hop/mesh quantitiesD2D); Support high-frequency PHY numerology for NX-D2D friendly D2D Takeadvantage of advanced antenna solutions and high processing capabilitiesand large storage available in devices RAT/frequencyselection/coordination Bring “sufficient” NW To do relay at L2 insteadof L3 type control into the D2D relay defined in Rel-13. Relaying UEsidelink management should appear to be similar (at L1/L2) to an out ofcoverage UE as a BS.

The NX design principles are applied to the D2D design as much aspossible to ensure a smooth integration into the NX system and to allowfor a gradual convergence between solutions for UL, DL, sidelink andpossibly also for backhaul links. Table 17 lists some of the NX designprinciples are applied for D2D, and also two additional ones (the lasttwo rows of the Table as above) as D2D-specific principles.

3.11.3 Spectrum for D2D and Duplexing Schemes

For LTE, D2D communication is supported in UL spectrum resources, in theUL band or UL subframes in the case of an FDD or TDD networkrespectively. The reasons for this decision are related to bothregulatory and implementation aspects.

However, NX is designed to flexibly manage UL/DL resources and utilizedifferent types of spectrum bands and therefore, NX D2D is also designedto be able to operate flexibly in UL as well as DL resources. Further,D2D should be able to operate both in licensed and unlicensed spectrumbands depending on the scenario, UE capabilities, coverage situation andother factors. For NX, the in higher frequency bands (>6 GHz), thenetwork will typically operate in TDD mode, whereas in lower frequencybands both FDD and TDD operations can be assumed. In FDD networks, theNX D2D link advantageously uses UL frequency resources, whereas in TDDnetworks, D2D operation is configured by the NW in line with theflexible duplex and dynamic TDD principles of NX.

In NX, the D2D sidelink is evolved such that the NX UL, NX DL, NXsidelink and backhaul links become similar in terms of PHY layercapabilities, including duplexing schemes. For proximity communication,that is when two devices are close to one another, bidirectional fullduplex can also be a viable duplexing scheme.

Operating in unlicensed and licensed bands may require that the sidelinkflexibly support scheduled and LBT type of MAC protocols (see section3.8).

3.11.4 Basic Architecture for D2D Communications: Clustering Concept

FIG. 161 illustrates D2D communications supported by the clusteringconcept. The CH node can be in NW coverage or out of NW coverage. A UEin coverage can act as a source for synchronization signals or provideRRM information to a CH which is outside NW coverage.

The NX D2D design uses clusters to support the broad diversity ofin-coverage, out-of-coverage and partial coverage use cases. The basicidea of the clustering is to extend the cellular concept to out ofcoverage situations by nominating a UE (handheld, truck mounted orprovisionally deployed) to act as a resource owner and control node,similarly to a regular eNB. The cluster head (CH) node is thus verysimilar to an eNB, although differences in capabilities in terms ofoutput power, number of UEs that it can support or mounted antennas canvary.

The CH, when outside NW coverage can get synchronization information orradio resource management information from a non-CH UE that is insidecoverage and capable of relaying such information from an eNB (FIG.161).

An inherent part of the cluster concept is the dynamic CH selectionprocess. The clustering concept is a hybrid of distributed (CHselection) and centralized (CH itself acting as a central node withinthe cluster) elements. In short, the CH selection process isdistributed, and uses discovery beacon signals transmitted from alldevices, including meaningful information about its status to be able tobe selected as a cluster head, and a selection of which peer device isto act as the cluster head for a particular device.

3.11.5 NX Network and UE Scenarios

FIG. 162 illustrates some combinations of NX deployment scenarios and UEcapabilities. In the NX standalone case (left), the UE supports NX,whereas in the co-deployed (middle) and multi-site (right) cases, theremay be a need for RAT selection for D2D.

As illustrated in FIG. 162, when NX is co-deployed or when NX and LTEare deployed at different sites, UEs with different RAT capabilities maybe in the proximity of one another such that D2D communication can be aviable alternative provided that these UEs use compatible RATs. Tofacilitate D2D communications in such scenarios, RAT selection for D2Dmay be a desirable function to fully exploit the proximity of variousdevices.

Such RAT selection does not necessarily imply selecting only one of theavailable interfaces at a time: RAT selection may also mean thesimultaneous usage of the available RATs as well. This can be the casein, for example, multihop scenarios.

3.11.6 Protocol Architecture

To support D2D in partial coverage and out-of-coverage situations,several design approaches can be viable, including a hierarchicalarchitecture or a distributed (flat) architecture as a design base. Ahybrid approach aims at electing a cluster head (CH) that takes asimilar role to an eNB in case the infrastructure becomes dysfunctional.In this approach the CH selection and re-selection are distributed inthe sense that nodes can elect the CH from among themselves without thehelp from a central entity. Once a CH is elected, it acts similarly toan eNB until re-selection.

When only group communications based on broadcast or multicast need tobe supported, the CH based architecture and associated dynamic clusterorganization procedures are not necessary. However, when point-to-pointD2D communications and the possibility to reach a cellular base stationthrough multiple hops are a requirement, the CH based approach canoutperform completely flat architectures.

3.11.6.1 General

The protocol stack for the sidelink is, when possible and when it can bemotivated, aligned with the protocol stack for the uplink/downlink. Forexample, a physical layer that is symmetric in uplink and downlink fitswell for D2D communication. As another example, a cluster head for D2Dcommunication may either be an eNB or a UE.

Moreover, the user plane protocol stack for different relaying casesinvolving a UE-UE direct interface (such as UE-to-network relay andUE-to-UE relay) should be aligned with any relaying cases forself-backhauling. Aligned protocol stacks have the following additionalbenefits:

-   -   RAN has the possibility to control which path that is used for a        given traffic flow, and consequently control which type of radio        resources that is used. This flexibility enables for example a        UE-UE user plane to be relayed via RAN, as well as a UE-NW user        plane to be relayed via a UE (acting as UE-to-NW relay),        controlled by RAN.    -   Moreover, there is an opportunity for RAN to switch a traffic        flow between different paths ensuring service continuity during        the switch since the switch would be performed on layer 2 level,        below the IP layer of the UE (like a handover). (To switch the        traffic between e.g., UE-network path and UE-to-network relay        path, the IP address used by the UE needs to be valid on both        paths, which requires support by the core network.)

FIG. 163 illustrates Layer 2 switching of user data paths.

3.11.6.2 User Plane

The user plane protocol architecture for the single hop case isillustrated in FIG. 164. For the relaying cases, the main approach is touse L2 relay. (L2 relay does not, in principle, preclude that L3 (IP)relaying is performed using a UE as an IP router.) This is also in linewith the main alternative for self-backhauling (see sections 3.6.6 and2.2.8.4). FIG. 165 illustrates the user plane protocol architecture forUE-to-network relay. In this figure, a two-layered RLC solution isassumed, as further described as one of the alternative approaches inSection 2.2.8.4.

FIG. 166 illustrates the user plane protocol architecture for UE-to-UErelay.

3.11.6.3 Control Plane

For D2D communication and discovery, there are three potential controlplanes:

-   -   A UE-Cluster Head control plane: Used to assign the radio        resources for D2D communication and discovery. In case the UE is        in coverage, the eNB takes the role of the cluster head. In case        the UE is outside coverage, a UE is selected as cluster head and        takes that role.    -   An end-to-end UE-UE control plane. This protocol is typically        not radio layer specific (“NAS”) and is used for mutual        authentication, setup of security and setup of bearer parameters        for the UE-UE end-to-end user plane. This protocol corresponds        to the PC5 Signaling Protocol specified for LTE-based D2D in        3GPP Rel-13. This control plane is connection-oriented, as        protocol contexts/states would be needed in each peer UE.    -   A link-by-link UE-UE control plane. This protocol is radio layer        specific and is used for the control of PHY, MAC and RLC        configuration used over a single hop between two UEs. It may        also be used for transfer of measurements on the UE-UE direct        radio link. This control plane is typically connection-oriented.    -   Moreover, there is also a control plane needed for direct        discovery, including multi-hop path discovery and relay        selection/reselection. This control plane can be included as        part of the end-to-end UE-UE control plane and/or link-by-link        UE-UE control plane above.

FIG. 167 illustrates plane protocols used by D2D (UE3 is outsidecoverage).

3.11.7 D2D Technology Components

FIG. 168 illustrates some combinations of NX deployment scenarios and UEcapabilities.

To realize the potential gains due to D2D communications, protect thenetwork from interference caused by sidelink transmissions, and tosmoothly integrate D2D operation in the NX system, some D2D specifictechnology components should be implemented in the network and devices.These are summarized in FIG. 168.

3.11.7.1 D2D Synchronization

The devices that participate in D2D (unicast, multicast and broadcast)communications should be synchronized in time and frequency. Goodsynchronization is necessary to ensure sidelink transmissions areaccording to the time/frequency domain scheduling decisions, energyefficient discovery and communication operation and facilitate highquality data reception. D2D synchronization can be challenging in out ofcoverage and partial coverage situations.

A concept of synchronization source (SynS) provided by a UE isapplicable to NX D2D. In LTE, D2D synchronization is facilitated by thePHY sidelink synchronization related procedures [TS 36.213]. A similardesign is the foundation for NX D2D synchronization procedures, whichcan be extended to out of coverage situations (Scenario 4) using theconcept of the SynS. A SynS can be a network node (BS), when available,or can be an in-coverage UE providing a synch signal to out-of-coverageUEs. The SynS can also be an out-of-coverage UE that obtainssynchronization with the help of another (e.g., in-coverage) UE.

3.11.7.2 Device and Service Discovery

Device and service discovery can be part of a D2D session or it can be astandalone service. In both cases, discovery implies that a UE can takeon the role of an announcing UE or a discovering UE or both announcingand discovering. In both cases, a prerequisite to starting the discoveryprocedure is service authorization and provisioning (See Section3.11.5.3.). Similarly to LTE, two discovery models are supported andconfigured by the network, taking into account UE capabilities, userpreferences, etc. Although these discovery models do not implydifferences at the physical layer, they can lead to differentperformance in terms of overall consumed energy and discovery time dueto the different beacon transmission patterns.

In the first discovery model (for LTE denoted ‘Model A’), the announcingUE broadcasts discovery messages on specific radio resources configuredby the network. Such network configuration can use broadcastinformation, preconfigured information and/or UE specific signaling(e.g., RRC signaling). The discovering UE can use the configurationinformation to capture and decode discovery messages in an energyefficient fashion, since it needs to monitor only the discoveryresources.

In the second model (for LTE denoted ‘Model B’), the discovering UE(rather than the announcing UE) broadcasts discovery messages, alsoaccording to configured and provisioned parameters and resources. Thenetwork assistance in the discovery procedures has been shown to bebeneficial both in terms of discovery time and overall used energyduring the discovery process.

In partial coverage and out-of-coverage situations, D2D discoverymechanisms depend on the basic architecture decisions regarding clusterbased or flat architecture for D2D communications. When clusters areused, the distributed CH selection and re-selection and CH associationprocedures act as discovery procedures based on node autonomous(distributed) decisions on transmitting and detecting beacon andsynchronization signals.

A special case of discovery is UE-to-Network relay discovery. A UE thatis authorized by the network to act as a relay for remote UEs typicallyout of coverage (or inside coverage) participates in UE-to-Network relaydiscovery during which a remote UE selects which UE to be used as theUE-to-Network relay.

Moreover, the discovery mechanisms for NX need to support path selectionfor more complex cases such as UE-to-UE relaying and multihop relaying.

3.11.7.3 Service Authorization and Provisioning

Service authorization and provisioning allows a device to use radio andother resources for D2D discovery and communication purposes. The exactmechanisms for this may depend on the D2D use case (see Section 3.11.1)and can include one or more of the following main elements:

-   -   Pre-configured information in the device. Preconfigured        information can contain the allowed frequency bands, associated        transmit power levels and other parameters that the device may        use for discovery and communication purposes. Pre-configuration        may take place prior to accessing the NX system and/or through        other accesses.    -   NAS signaling to exchange information with CN functions similar        to the LTE ProSe function.    -   System information and UE specific (e.g., RRC) signaling when in        NX coverage.

3.11.7.4 Sidelink Management

Sidelink management is responsible for the establishment, maintenanceand termination of sidelink channels, including discovery andcommunication channels. These functions can be considered as theextensions and evolution of functions that are defined in LTE in [TS36.213].

Examples on sidelink management include the triggering of broadcastdiscovery (announcing or inquiry) messages, establishing the sidelinkshared channel with a specific peer device or triggeringbroadcast/multicast messages to a set of peer UEs on specific resources,etc.

FIG. 169 illustrates examples of sidelink management functions.

3.11.7.5 Measurement Reports and Radio Resource Management

FIG. 170 illustrates examples of measurement functions desirable for D2Dcommunications.

Measurements and associated reporting provide important input tosidelink management and D2D related radio resource management functionsso that D2D communication can indeed improve the overall spectral/energyefficiency and coverage and reduce latency without causing unacceptableinterference to cellular traffic. The radio resource managementfunctions that are desirable to realize these goals depends on the usecase (see Section 3.11.1), availability of licensed/unlicensed spectralresources, traffic load, device capabilities (e.g., small battery drivendevice, smart phone, public safety device). The RRM functions aredistributed between network nodes and the devices. Important aspects ofthe functional distribution between network nodes and devices are thelevel of network control and the time scale over which network anddevice RRM functions operate. The general principle for these aspects isthat the network or the CH has tight control over resources owned bynetwork or by the CH (e.g., licensed spectrum resources). Accordingly,two UEs, out of which none of them is CH capable, cannot communicate onlicensed resources when out of coverage.

The RRM functions that are desirable for D2D communications involvestandardized and proprietary elements and can partially reuse RRMfunctions designed for traditional cellular communications. Such RRMfunctions include one or more of:

-   -   Mode selection between cellular and direct D2D mode;    -   Sidelink resource allocation and scheduling;    -   Sidelink power control;    -   Out-of coverage and partial coverage cluster formation.

3.11.7.6 Multi-Antenna Schemes (UE Beamforming, Sidelink Beam Matching)

FIG. 171 illustrates how UE beamforming for D2D communications relies onnetwork controlled service authorization, provisioning and localmeasurements. The eNB/CH control is at a much coarser time scale (˜500ms) than the D2D link control exercised autonomously within theconstraints set by the eNB/CH.

UE beamforming can largely improve the D2D range and therefore canfurther improve the potential of D2D communications for, e.g., cellularcoverage extension, increasing the number of devices reached by devicediscovery or reducing the number of devices needed to provideprovisional coverage in a disaster situation. From a configuration andcontrol perspective, the basic principle for supporting UE beamformingis similar to other device functions (see 3.11.7.3 and 3.11.7.5): thedevice operation relies on the service provisioning and configurationinformation and the supporting measurement procedures.

3.11.7.7 D2D Band Selection Strategy

For cases with multiple available bands, such as licensed andnon-licensed bands, a negotiation and decision making strategy should beimplemented to improve the balance of overall bandwidth efficiency andspecific link benefits of side-links. For instance, high or lowerfrequency bands have distinct physical characteristics such as differentpropagation loss, bandwidth availability, coherent time of channels,spatial separation granularity. These aspects could be prudentlyconsidered for different D2D cases in term of different QoSrequirements, link budgeting situation, interference status, etc. Ifmulti-bands are available, optimized and dynamic choice of the bandselection impacts substantially on D2D link-wise performance and NW-wiseoverall performance.

In practice, multiple mode UE devices are pervasively available.Integrating such modes and bands provides more opportunity to balanceindividual link performance and NW performance targets which is of aspecial interest to D2D cases to further extend the D2D capacity gains.

The strategy of band selection can take many factors into account, suchas NW loading, non-licensed band availability and quality, commoncapability of UE pairs, side-link quality for different bands, latencyrequirement of traffic, side-link role as relay or directcommunications, UEs' roles in wireless relay or simple single role as adestination/source of traffic.

At different bands, the UE or eNB may have a different MAC mode, whichis optimized for this specific band. Namely, one node capable ofoperating at different radio resource partition possesses a multi-modeMAC transiting from one to another. Resource partitioning enables asimplified D2D integration to cellular access; Potentially, it may bringindispensable robustness for dense NW deployment and high loading casesand easy feature depreciation or adding-in for NX cellular NW with D2D.

3.11.7.8 D2D Scheduling, HARQ and DRX

FIG. 172 illustrates a sidelink scheduling operation.

L2 mechanisms proposed for D2D should enable energy-efficient, lowlatency and high reliability communications for both in-coverage andout-of-coverage scenarios e.g., by adopting the necessary L2 mechanismse.g., DRX and HARQ.

The fast scheduling (small time scale operation) of the sidelink ismanaged autonomously by the devices, within the constraints configuredby an eNB or by CH as shown in FIG. 172. Examples of sidelink operationsconfigured by an eNB or CH include D2D slow (spectrum allocation,maximum transmit power etc.) scheduling, HARQ processes and DRXmanagement.

Due to the fact that the eNB scheduling requires additional networkprocessing and two hop message exchange for D2D scheduling, thedisjunction of scheduling is used for D2D transmissions when anin-coverage scenario is assumed. This means that each D2D UE isresponsible for its own transmission, and for each transmission, thefast scheduling information, which is a subset of slow scheduling grant,is self-contained within the sidelink transmission in order to enablefrequency selective scheduling. It should be also noted that uplink andsidelink resource reuse (for the same UE) would be possible if that isjointly and semi-persistently configured by the eNB.

FIG. 173 illustrates sidelink HARQ operation. Similarly to NX DL HARQ(see Section 2.2.7.2 for further details), HARQ feedback can be sent asa sidelink MAC control element. By embedding HARQ feedback in MAC, itbecomes CRC protected and ACK/NACK detection error can be minimized.

FIG. 174 illustrates DRX alignment of infrastructure-to-device (I2D) andD2D communications for maximizing OFF-duration. D2D-DRX and cellular-DRX(C-DRX) may be independent DRX mechanisms. Both configurations may onlybe visible to the CH. Therefore, the CH can align the D2D-DRX withC-DRX, when D2D and infrastructure-to-device (I2D) transmissions happen,so as to minimize the energy consumption by switching off morecomponents of the terminal transceiver.

3.11.8 Mobility Aspects of D2D Communication

When it comes to mobility management, section 3.5 describes thebeam-based mobility solution, yet for D2D connections, there are twomain issues to be further discussed:

-   -   Change from maintaining single UE specific connection to more        than one UE: traditionally, when there is a change of serving        network node, the resource allocation to the moving UE may be        reconfigured. However, this kind of resource allocation has to        take into account of the status of the counterpart UE(s)        evolving in the D2D communication, in order to minimize the D2D        serving interruption due to the resource reconfiguration. This        may require some enhancement on the cellular-oriented mobility        management procedure.    -   The D2D communication in RRC dormant state (which is defined in        Section 2.1): In this state, the resource usage of D2D link is        controlled by UE themselves (although still within the resource        pool defined by network using broadcast signaling), so when the        UE movement is beyond the network node range, the resource        configuration change cannot be known by the counterpart D2D        UE(s) via network nodes. Therefore, in order for        seamless/lossless switching, the resource re-configuration has        to be notified to the counterpart UEs via D2D signaling over D2D        control plane, which is to be enhanced to achieve that.

3.11.8.1 D2D-Aware Handover

FIG. 175 illustrates D2D cluster communicating over the cell borders. Incase of in-coverage use cases where the eNB is the CH, RRC signallingfor D2D control needs to be exchanged between D2D cluster and eNB inorder to enable a reliable control plane and robust mobility. In thiscase, it may be costly for network to manage the control plane of a D2Dcluster with multiple eNBs, due to the fact that the backhaul overheadin the radio network may be an issue. Therefore, it is beneficial tokeep the control plane of D2D cluster under a single eNB. This isachieved by managing the mobility of a D2D cluster based on not only thechannel quality of a single device but also the measurements from otherdevices in the cluster. This mechanism can be implemented on the networkside by simply defining an additional handover criterion. Note that thecomplexity may increase if the optimal node needs to be selected for theD2D control since the coordinated measurement reporting (and theadditional measurement configuration and reporting thereof) are thenrequired.

3.12 Architecture Aspects of NX Multi-Point Connectivity

This section describes architecture solutions for supporting NXmulti-point connectivity. The section is organized as follows: InSection 3.12.1, a brief background and motivation for multi-pointconnectivity is provided. Section 3.12.2 describes the higher layerprotocol architecture for multi-point connectivity for NX. Section3.12.3 elaborates on some multi-connectivity specific aspects ofmobility. Then, Section 3.12.4 describes a method that can be used torelax the backhaul latency requirements by applying UE assistedmulti-point diversity.

3.12.1 Background

NX is likely to be deployed in bands higher than those of currentcommercial RANs. At higher frequencies, shadowing of radio paths is muchmore severe as compared to radio shadowing at lower frequencies.Especially for high frequencies, line-of-sight may be needed forsuccessful transmission. In such radio conditions, multi-pointconnectivity can be used to reduce interruptions in traffic. Capacityand user throughput improvements can also be achieved when multipleconnection points can be maintained simultaneously. The NX designsupports multi-point connectivity as an integral part of the concept. Asdiscussed above, the DL mobility concept of NX is beam-based. From a UEpoint of view, the mobility procedures are the same, independently onhow many eNBs that are involved. A consequence of this is that the UEdoes not have to care about which eNB is transmitting beams or not;sometimes this is referred to as the UE being node-agnostic and themobility being UE-centric. For mobility to work efficiently, theinvolved eNBs need to maintain beam neighbor lists, exchange beaminformation, and coordinate MRS usage. The generic mobility approach forNX is described in Section 3.5. Fast switching of beams in a multi-pointconnectivity scenario requires fast communication between eNBs and mayalso require pre-caching and duplication of data; in many cases the dataneed to be duplicated and distributed to, and from, multiple eNBs. Thisrequirement challenges the capability of backhaul connection in terms ofcapacity and delay. One option is to put a certain data splitting agencyat EPC side so as to remove the loop at anchor-eNB S1 connection.Additionally, at air-interface, it is possible to reduce transmissionpossibility/ratio of such duplicated data between eNBs via an UEassisted flow control. Subsection 3.12.5 discuss that UE assistance inthis regard can maximize multiple-point diversity performance.

In FIG. 176, the relation between different multi-connectivity modes inNX is illustrated. The connected transmission points can belong to oneor multiple eNBs, typically referred to as intra-eNB multi-pointconnectivity and inter-eNB multi-point connectivity, respectively.

Different transmission/reception modes can be considered depending onthe channel conditions, network deployment, available backhaul capacityand delay, and type of traffic. In the NX context, multi-point diversity(MPD), traffic aggregation and distributed MIMO are issues. Trafficaggregation usually refers to multi-connectivity operations at lowerlayers being independent and distinct in terms of resources and/or RATs,such as carrier aggregation or IP layer aggregations. Distributed MIMOinvolves multiple transmission points and assumes joint coding over thebranches. Typically, it requires a backhaul with high capacity and lowdelay to deliver the expected performance. In this section the focus ison architecture and protocol aspects of multi-point diversity (MPD), andtraffic aggregation.

Coordinated multi-point (CoMP) is a term that is used to describe a setof specific LTE features used for intra LTE multi-point connectivity.Usually, CoMP features tight coordination on MAC level. MAC coordinationis desirable when co-channel radio resources are used for the differenttransmission points. The term CoMP is intentionally avoided in the NXcontext to avoid confusion.

Alongside measurement acquisition, a challenge associated withmulti-point connectivity lies in limitations on capacity and delay inthe backhaul links carrying the inter node interfaces. In manydeployments, backhaul with limited capacity and large latency is theonly option due to high cost involved in deploying fast backhaul. Forexample, in some cases, X2 connections are made available by an ordinaryinternet data link.

The multi-connectivity described in this section focus on the inter eNBcase. The multi-connectivity solution for intra-eNB where eNB comprisesa centralized RRC/PDCP and distributed RLC/MAC is an alternativeembodiment.

3.12.2 Protocol and Architecture of Multi-Point Connectivity in NX3.12.2.1 User Plane Protocol Architecture

Multi-point connectivity on the user plane can operate at differentlayers. The integration layer for multi-point connectivity can be eitherPHY layer, MAC layer (which corresponds to Carrier Aggregation in theLTE context), or PDCP layer (which corresponds to Dual Connectivity inLTE) as mentioned in Section 3.7. In this section, the investigatedmulti-point connectivity solutions work at PDCP layer. This solution isviable also for slow backhaul, and in alignment with the proposal insection 3.7 for NX and LTE interworking. Other multi-point connectivitysolutions, e.g., inter-node MAC split multi-point connectivity are alsopossible approaches. Inter-node MAC split is preferred considering thecentralized RRC/PDCP architecture and fast backhaul. In this section,slow backhaul and PDCP spit are assumed. The user plane protocol stackfor NX multi-point connectivity is shown in FIG. 177, taking two SeNBsas an example. It is suitable for both multi-point diversity andmulti-point traffic aggregation modes.

3.12.2.2 Control Plane Protocol Architecture Alternatives

Section 3.7 discusses the RRC design for LTE and NX tight integration.Here the focus is on intra NX multi-point connectivity using PDCP as theintegration layer. The question in focus is whether to have onecentralized RRC entity in MeNB (Master eNB), which is termed asalternative 1 below, or multiple RRC entities distributed in both MeNBand each SeNB in multi-point connectivity, which is termed asalternative 2 below. (MeNB is the anchor point for UE from CN (corenetwork) point of view and the radio link between MeNB and UE determineUE RRC state. SeNB assists MeNB to serve UE either to increase UEthroughput or increase the radio link robustness between UE and RAN.)

The alternative 1 is similar to that defined for DC in LTE with someextensions. Beside one MeNB, more than one SeNB are involved inmulti-point connectivity. There is only one RRC entity located at MeNBwhich communicate with the RRC entity at UE. When SeNB RRM functionneeds to configure its local radio resources between it and UE, SeNBneeds to first encapsulate its RRC message into an X2 message andtransmit it via backhaul to MeNB. And then MeNB forwards RRC messagefrom SeNB to UE. Similarly, when UE sends measurement report, even thismeasurement report is SeNB related, this message is received by MeNB.MeNB then checks the measurement report, if some of the information isrelated to SeNB, composes a new message and forwards it to SeNB viabackhaul. The RRC diversity solution can be supported in thisalternative which means RRC message from MeNB can be transmitted to UEvia multiple legs to increase the robustness of signaling transmissions.The protocol architecture for alternative 1 is shown in FIG. 178, whichillustrates that there one RCC entity at the MeNB.

An advantage of this alternative is that it is simple, compared toalternative 2 (discussed below) and follow the same architecture as LTEDC. The UE only needs to maintain one RRC connection with MeNB, and itis not impacted by DL and UL decoupling. A disadvantage is that theresponse to some radio resource configuration at SeNB, e.g., UE beamswitching within SeNB, may be slow, and when MeNB crashes the procedureto recover the whole multi-point connectivity could also relatively timeconsuming compared to alternative 2.

In alternative 2, multiple RRC entities are setup at MeNB and SeNBs, asshown at FIG. 179. The RRC entity at SeNB can communicate with the RRCentity at UE. There is only one RRC state between UE and the multi-pointconnectivity which is determined by the RRC connection between UE andMeNB. The RRC at MeNB is a full stack RRC which can execute all RRCfunctionalities while the RRC at SeNB is a slim RRC which can onlyexecute limited RRC functionalities, e.g., RRC connectionreconfiguration can be executed to configure the radio resources betweenSeNB and UE, but RRC connection setup and release are excluded. Theprotocol architecture of alternative 2 is shown in FIG. 179.

An advantage of this alternative is that it can react fast to localradio resource configuration events between SeNB and UE. When MeNBcrashes, assuming the connection between UE and SeNB is maintained, thetime to recover the multi-point connectivity could be short if SeNBalready has RRC related UE context e.g., security KEY stored plus S1related UE context, e.g., S1AP UE ID. So either UE or SeNB, which takesthe role as new MeNB, can send RRC message to its peer directly to takeaction without requiring re-establishment of the RRC connection. And theSeNB which is going to become a MeNB can also inform CN that it is thenew MeNB to restore S1 connection. A disadvantage of this alternative isthat it is more complicated. Since multiple network nodes can send RRCmessage to UE, several issues need to be solved. First, SRB (SignalingRadio Bearer) needs to be setup between each SeNB and UE. The securitykey used for the SRB between SeNB and UE need be configured by MeNBduring the setup procedure. Second, the SRB between SeNB and UE need beconfigured with a unique logical channel ID within the multi-pointconnectivity so that UE can know from which node a RRC message comes andthen deliver a response RRC message back according to the mappingrelationship between logical channel ID and network node. Third, the UEinternal RRC procedure handling needs to be enhanced to support parallelRRC procedures. That is, the RRC procedure from SeNB and MeNB can beexecuted concurrently. There may be a risk that the RRC request fromMeNB and SeNB conflict with each other, e.g., the total flows to receiveconfigured by network may exceed UE capability. If so, UE can reportback to, e.g., SeNB that the total configured flows are over itscapacity. After receiving this information, SeNB can reconfigure itsmessage to UE to meet UE capability.

Since the alternative 1 is a centralized RRC protocol architecture, itis better that beam switching scheme could work at Layer 2 so that beamswitching related command and message can be exchanged between SeNB andUE directly without requiring the involvement of MeNB. For alternative2, it suits the beam switching scheme working on either Layer 2 or Layer3, as mentioned in Section 3.5.

3.12.3 Architecture Aspects of Mobility for Multi-Point Connectivity

The signaling procedures on L3 for multi-point connectivity in NXinclude SeNB addition, SeNB release, SeNB change, SeNB modification,MeNB change, MeNB and SeNB role switch. For the procedure involving justSeNB, if different frequencies are used in multi-point connectivity,then the criterion and trigger condition for the procedures could besimilar to that of LTE DC—an SeNB with good radio quality can be addedinto multi-point connectivity, and correspondingly an SeNB with worseradio quality can be released from multi-point connectivity. If singlefrequency is used in multi-point connectivity, which SeNB to add orrelease from multi-point connectivity need to consider the interferenceimpact into this multi-point connectivity besides just radio channelquality which needs further investigation.

For MeNB change (a new eNB outside this multi-point connectivity becomesa new MeNB, and SeNB does not change), or MeNB and one SeNB switchroles—one SeNB switches to new MeNB and MeNB switches to new SeNB, theprocedure defined in LTE DC is quite cumbersome: UE needs to firstremove all SeNB in the multi-point connectivity, handover from old MeNBto new MeNB, then setup SeNB in new multi-point connectivity again.Since all the members in the multi-point connectivity are not changedafter role switch, a fast and efficient procedure can be defined, asshown in FIG. 180.

That is, before role switch, the security KEY to be used between theSeNB (which will be upgraded to MeNB) and UE is also configured. UEmaintains multiple security contexts. When role switch occurs, signalingbetween involved eNBs indicates this is a role switch, so that all theexisting protocol entities and context in eNBs can be reused during roleswitch as much as possible. No additional L3 RRC signaling is needed toinform UE this role switch (updating of timing advance etc. are doneindependently of the role switch). Packet forwarding may be needed fromold MeNB to new MeNB after role switch.

For link level related mobility, it includes add/remove/change of theserving links for a UE in multi-point connectivity. Depends on UEcapability in communicating with multiple eNB in multi-pointconnectivity, and the network deployment, link level mobility could meanUE transmit/receive data using multiple links or legs concurrently, UEtransmit/receive data using just one link/leg concurrently and fastswitch within these links/legs or a combination. For example, onelink/leg is always used for data transmission/reception, otherslinks/legs are dynamically switched from one to the other.

3.12.4 Fast UE-Assisted Multi-Point Diversity for NX Radio Access

As mentioned in 3.12.1, both S1 and X2 connections between eNBs and EPCor inter-eNBs are usually made by non-dedicated cabling through ordinaryinternet connections. The resulting non-ideal backhaul capacity anddelay performance becomes a bottleneck to performance gains bymulti-point diversity. Facing this reality, this section introduces amethod that can be used to speed up the control plane coordination whenthe backhaul is slow and the integration layer is on PDCP. An importantidea of fast UE-assisted multi-point diversity is to employ UEassistance, or even a UE decision, to assist the MAC procedure, in orderto speed-up MAC coordination between the involved eNBs.

An objective of this section is to propose a solution on multi-pointdiversity (MPD), for which it assumes: (i) A scenario of realisticnon-ideal backhaul, (ii) Both downlink (DL) and uplink (UL) MPDdiversity schemes are considered. (iii) Access links involved operate atthe same frequency band. Hence, it is a scheme of intra-frequencymulti-point diversity. Owing to aforementioned reasons, it has a wideapplicability in reality.

In contrast to intra-carrier multi-point connectivity using relaxedbackhaul for coordination, this approach relies on air-interface basedcoordination through assistance or decision of UE. Therefore, it can, inmany cases, achieve lower control plane latency than coordinationschemes relying on (relaxed) backhaul.

Note that this approach is still subject to backhaul latency impact onuser plane delay, since the user plane data is still delivered viarelaxed backhaul.

This design primarily includes two parts: (i) UE assisted MAC and (ii)UE assisted flow control, these two parts can work standalone or jointlyto enhance the multi-point diversity gain. A generic description is that‘pre-grant’ from NW and UE's decision & acknowledgement of the“pre-grant” plays a role in the operation. Firstly, the concept of UEassisted MAC is based on the fact that the UE owns timely information onlink quality states itself so that it is suitable to dynamically conductthe resource coordination (in contrast to traditional DC scheme whichrelies on BH to do the coordination). It is proposed that the UEacknowledgement or rejection on “pre-grant” from the NW, aids thenetwork to fast change resource share among each links to adapt todiverse link quality variations for links with the same frequency band.

Secondly, the main concept of UE assisted flow control is to introducethe decision entity at UE for the UE decision based flow control. Theinput information is obtained by UE local measurement, and UE makes thedecision/suggestion on the PDU delivery routing on the multipleconnectivity and send commands to each serving AP directly.

4 Discussion of Selected Terms 4.1 Antennas

Antenna port—An antenna port is defined such that the channel over whicha symbol on the antenna port is conveyed can be inferred from thechannel over which another symbol on the same antenna port is conveyed.

In practice a reference signal and an “antenna” as seen by the receiver.Two antenna ports are said to be quasi co-located if the large-scaleproperties of the channel over which a symbol on one antenna port isconveyed can be inferred from the channel over which a symbol on theother antenna port is conveyed.

Example: Cross-polarized beam=set of two antenna ports, mapped to twoorthogonal polarizations, with QCL assumed wrt delay spread, Dopplerspread, Doppler shift [list not exhaustive]

Beam—A beam is a set of beam weight vectors, where each beam weightvector has a separate antenna port, and all the antenna ports havesimilar average spatial characteristics. All antenna ports of a beamthus cover the same geographical area. Note however, that the fastfading characteristics of different antenna ports may be different. Oneantenna port is then mapped to one or several antenna elements, using apossibly dynamic mapping. The number of antenna ports of a beam is therank of the beam.

4.2 Latency

Control plane latency—Control plane (C-Plane) latency is typicallymeasured as the transition time from different connection modes, e.g.,from idle to active state.

RAN User plane latency—The RAN user plane latency (also known asRadio-specific delay) is defined as the one-way transit time between anSDU packet being available at the IP layer in the user terminal/basestation and the availability of this packet (protocol data unit, PDU) atIP layer in the base station/user terminal. User plane packet delayincludes delay introduced by associated protocols and control signalingassuming the user terminal is in the active state.

Mobile Network User Plane Latency—The Mobile Network or PLMN user planelatency is defined as the one-way transit time between an SDU packetbeing available at the IP layer in the user terminal/Network Gateway andthe availability of this packet (protocol data unit, PDU) at IP layer inthe Network Gateway/user terminal. PLMN packet delay includes delayintroduced by all transport tunnels that are controlled by the networkoperator, including a virtual network operator using physicalinfrastructure that is owned by a third party.

Application end-to-end delay—Application end-to-end delay represents theone-way transit time including framing delay and buffering delay at thesource and all intermediate application-aware processing nodes duringthe transit of a packet or stream of packets between a service orsoftware application on a terminal/server node communicating withanother terminal or server node. Application delay is scenario specificand may include framing of information, transcoding or translationservices, and network delays. In rare occasions where the applicationdepends on two-way interactive communication, it may have to account forround-trip time.

Application jitter—Application jitter with respect to min delaycorresponds to the variation in delay from a minimum value, and ismeasured using statistical expectation of the difference betweeninstantaneous delay and the minimum possible delay. Application jitterwith respect to mean delay logically follows.

4.3 Reliability and Service Availability

For 5G new use cases are foreseen in the area of critical machine-typecommunication, which is referred to by ITU as ultra-reliable and lowlatency communication. Example use cases are distribution automation inthe smart power grid, industrial manufacturing and control, autonomousvehicles, remote control of machines, tele-surgery. For these use casesthe requirements of reliability and availability are used, which wedefine in this section. The typical applications are control processes,which typically operate with some sort of a feedback loop and sensoryinput directing an actuator and depend on “deterministic” behavior ofthe underlying communication system. The reliability defines to whatlevel the deterministic behavior can be met, e.g., the desiredinformation is successfully received at the right time.

Reliability—The reliability of the connectivity is the probability thata message is successfully transmitted to a receiver within a specifieddelay bound. For example, the reliability may require that, controlmessages are delivered to the receiver with a 99.9999% guarantee andwithin a delay of 1 ms. This means that only 0.0001% of packets areeither lost due to transmission errors or are delayed due to congestionor load on the channel, or too low achievable data rate. Thisreliability is provided with regard to a maximum message size, so thelatency can be linked to a required data rate. The reliability relatesto the reliability of the connectivity provided from the sender to thereceiver; the connectivity can be provided by a single radio link, butalso by a set of radio links (e.g., on different frequency layers, withdifferent antenna sites, or even based on different RATS) that jointlyprovide the connectivity. The reliability requires that a sufficientamount of radio resources is available for a transmission atsufficiently high SNR on the connectivity links. The SNR must enable theradio link to meet the required data rate and delay bound and alsoprovide sufficient fading margins for the desired reliability level.

Service availability—For a certain reliable-low-latency service—a pairof reliability and latency bound—a service-availability can be defined,which defines to what level the reliability-latency is provided in spaceand time. In bounded environments high availability can be required,e.g., via a service layer agreement. For example, in an industrial plantan availability of e.g., 99.9999% can be specified, so that at 99.9999%of transmissions in time and space fulfil the reliability-delayrequirements within the premises of the plant. This can be enabled bycorresponding deployment and redundancy of the network. (The SLA may befurther limited to a e.g., a maximum number of devices in the area or amaximum aggregate priority traffic load.) In spatially unboundedenvironments, like connected vehicles autonomously driving aroundanywhere on a continent, an availability cannot be easily guaranteedwith any deployed infrastructure. Even with ad-hoc D2D communicationbetween vehicles, the availability of a reliable-low-latency-service canonly be provided for a certain range around the transmitter and possiblywith further restrictions of a maximum vehicle density (and prioritytraffic load).

It should be noted that many control systems that requirereliable-low-latency services can have several operation modes,depending on the connectivity reliability and delay. For example, aplatoon of autonomously driving trucks may drive with 4 m inter-vehicledistance if the communication can be 99.9999% guaranteed within 5 ms,and may switch to an 8 m inter-vehicle distance if only a delay of 10 msat 99% reliability can be provided. Similarly, the control cycle of aproduction plant can be reduced, or a remote-controlled machinery mayonly operate in a conservative control mode for inadequatereliability-delay levels. It is desirable that the communication systemcan inform a service about changes in the achievable service level sothat the application may adapt. This concept is sometimes referred to asreliable service composition, where changes in service level areindicated in an availability indication.

5 Methods, Radio Network Equipment, and Wireless Devices

In this section, some of the many detailed techniques and proceduresdescribed above are generalized and applied to specific methods, networknodes, and wireless devices. Each of these methods, radio networkequipment, and wireless devices, as well as the numerous variants ofthem that are described in the more detailed description above, may beregarded as an embodiment of the present invention. It should beunderstood that the particular groupings of these features descriedbelow are examples—other groupings and combinations are possible, asevidenced by the preceding detailed discussion.

Note that in the discussion that follows and in the claims appendedhereto, the use of labels “first,” “second,” “third,” etc., is meantsimply to distinguish one item from another, and should not beunderstood to indicate a particular order or priority, unless thecontext clearly indicates otherwise.

5.1 Wireless Devices and Methods

As used herein, “wireless device” refers to a device capable,configured, arranged and/or operable to communicate wirelessly withnetwork equipment and/or another wireless device. In the presentcontext, communicating wirelessly involves transmitting and/or receivingwireless signals using electromagnetic signals. In particularembodiments, wireless devices may be configured to transmit and/orreceive information without direct human interaction. For instance, awireless device may be designed to transmit information to a network ona predetermined schedule, when triggered by an internal or externalevent, or in response to requests from the network. Generally, awireless device may represent any device capable of, configured for,arranged for, and/or operable for wireless communication, for exampleradio communication devices. Examples of wireless devices include, butare not limited to, user equipment (UE) such as smart phones. Furtherexamples include wireless cameras, wireless-enabled tablet computers,laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USBdongles, and/or wireless customer-premises equipment (CPE).

As one specific example, a wireless device may represent a UE configuredfor communication in accordance with one or more communication standardspromulgated by the 3rd Generation Partnership Project (3GPP), such as3GPP's GSM, UMTS, LTE, and/or 5G standards. As used herein, a “userequipment” or “UE” may not necessarily have a “user” in the sense of ahuman user who owns and/or operates the relevant device. Instead, a UEmay represent a device that is intended for sale to, or operation by, ahuman user but that may not initially be associated with a specifichuman user. It should also be appreciated that in the previous detaileddiscussion, the term “UE” is used, for convenience, even more generally,so as to include, in the context of the NX network, any type of wirelessdevice that accesses and/or is served by the NX network, whether or notthe UE is associated with a “user” per se. Thus, the term “UE” as usedin the above detailed discussion includes machine-type-communication(MTC) devices (sometimes referred to as machine-to-machine, or M2Mdevices), for example, as well as handsets or wireless devices that maybe associated with a “user.”

Some wireless devices may support device-to-device (D2D) communication,for example by implementing a 3GPP standard for sidelink communication,and may in this case be referred to as D2D communication devices.

As yet another specific example, in an Internet of Things (IOT)scenario, a wireless device may represent a machine or other device thatperforms monitoring and/or measurements, and transmits the results ofsuch monitoring and/or measurements to another wireless device and/or anetwork equipment. A wireless device may in this case be amachine-to-machine (M2M) device, which may in a 3GPP context be referredto as a machine-type communication (MTC) device. As one particularexample, a wireless device may be a UE implementing the 3GPP narrow bandinternet of things (NB-IoT) standard. Particular examples of suchmachines or devices are sensors, metering devices such as power meters,industrial machinery, or home or personal appliances, e.g.refrigerators, televisions, personal wearables such as watches etc. Inother scenarios, a wireless device may represent a vehicle or otherequipment that is capable of monitoring and/or reporting on itsoperational status or other functions associated with its operation.

A wireless device as described above may represent the endpoint of awireless connection, in which case the device may be referred to as awireless terminal. Furthermore, a wireless device as described above maybe mobile, in which case it may also be referred to as a mobile deviceor a mobile terminal.

Although it will be appreciated that specific embodiments of thewireless devices discussed herein may include any of various suitablecombinations of hardware and/or software, a wireless device configuredto operate in the wireless communications networks described hereinand/or according to the various techniques described herein may, inparticular embodiments, be represented by the example wireless device1000 shown in FIG. 181.

As shown in FIG. 181, example wireless device 1000 includes an antenna1005, radio front-end circuitry 1010, and processing circuitry 1020,which in the illustrated example includes a computer-readable storagemedium 1025, e.g., one or more memory devices. Antenna 1005 may includeone or more antennas or antenna arrays, and is configured to send and/orreceive wireless signals, and is connected to radio front-end circuitry1010. In certain alternative embodiments, wireless device 1000 may notinclude antenna 1005, and antenna 1005 may instead be separate fromwireless device 1000 and be connectable to wireless device 1000 throughan interface or port.

Radio front-end circuitry 1010, which may comprise various filters andamplifiers, for example, is connected to antenna 1005 and processingcircuitry 1020 and is configured to condition signals communicatedbetween antenna 1005 and processing circuitry 1020. In certainalternative embodiments, wireless device 1000 may not include radiofront-end circuitry 1010, and processing circuitry 1020 may instead beconnected to antenna 1005 without radio front-end circuitry 1010. Insome embodiments, radio-frequency circuitry 1010 is configured to handlesignals in multiple frequency bands, in some cases simultaneously.

Processing circuitry 1020 may include one or more of radio-frequency(RF) transceiver circuitry 1021, baseband processing circuitry 1022, andapplication processing circuitry 1023. In some embodiments, the RFtransceiver circuitry 1021, baseband processing circuitry 1022, andapplication processing circuitry 1023 may be on separate chipsets. Inalternative embodiments, part or all of the baseband processingcircuitry 1022 and application processing circuitry 1023 may be combinedinto one chipset, and the RF transceiver circuitry 1021 may be on aseparate chipset. In still alternative embodiments, part or all of theRF transceiver circuitry 1021 and baseband processing circuitry 1022 maybe on the same chipset, and the application processing circuitry 1023may be on a separate chipset. In yet other alternative embodiments, partor all of the RF transceiver circuitry 1021, baseband processingcircuitry 1022, and application processing circuitry 1023 may becombined in the same chipset. Processing circuitry 1020 may include, forexample, one or more central processing units (CPUs), one or moremicroprocessors, one or more application specific integrated circuits(ASICs), and/or one or more field programmable gate arrays (FPGAs).

In particular embodiments, some or all of the functionality describedherein as relevant to a user equipment, MTC device, or other wirelessdevice may be embodied in a wireless device or, as an alternative, maybe embodied by the processing circuitry 1020 executing instructionsstored on a computer-readable storage medium 1025, as shown in FIG. 181.In alternative embodiments, some or all of the functionality may beprovided by the processing circuitry 1020 without executing instructionsstored on a computer-readable medium, such as in a hard-wired manner. Inany of those particular embodiments, whether executing instructionsstored on a computer-readable storage medium or not, the processingcircuitry 1020 can be said to be configured to perform the describedfunctionality. The benefits provided by such functionality are notlimited to the processing circuitry 1020 alone or to other components ofthe wireless device, but are enjoyed by the wireless device as a whole,and/or by end users and the wireless network generally.

The processing circuitry 1020 may be configured to perform anydetermining operations described herein. Determining as performed byprocessing circuitry 1020 may include processing information obtained bythe processing circuitry 1020 by, for example, converting the obtainedinformation into other information, comparing the obtained informationor converted information to information stored in the wireless device,and/or performing one or more operations based on the obtainedinformation or converted information, and as a result of said processingmaking a determination.

Antenna 1005, radio front-end circuitry 1010, and/or processingcircuitry 1020 may be configured to perform any transmitting operationsdescribed herein. Any information, data and/or signals may betransmitted to a network equipment and/or another wireless device.Likewise, antenna 1005, radio front-end circuitry 1010, and/orprocessing circuitry 1020 may be configured to perform any receivingoperations described herein as being performed by a wireless device. Anyinformation, data and/or signals may be received from a networkequipment and/or another wireless device

Computer-readable storage medium 1025 is generally operable to storeinstructions, such as a computer program, software, an applicationincluding one or more of logic, rules, code, tables, etc. and/or otherinstructions capable of being executed by a processor. Examples ofcomputer-readable storage medium 1025 include computer memory (forexample., Random Access Memory (RAM) or Read Only Memory (ROM)), massstorage media (for example, a hard disk), removable storage media (forexample, a Compact Disk (CD) or a Digital Video Disk (DVD), and/or anyother volatile or non-volatile, non-transitory computer-readable and/orcomputer-executable memory devices that store information, data, and/orinstructions that may be used by processing circuitry 1020. In someembodiments, processing circuitry 1020 and computer-readable storagemedium 1025 may be considered to be integrated.

Alternative embodiments of the wireless device 1000 may includeadditional components beyond those shown in FIG. 181 that may beresponsible for providing certain aspects of the wireless device'sfunctionality, including any of the functionality described hereinand/or any functionality necessary to support the solution describedabove. As just one example, wireless device 1000 may include inputinterfaces, devices and circuits, and output interfaces, devices andcircuits. Input interfaces, devices, and circuits are configured toallow input of information into wireless device 1000, and are connectedto processing circuitry 1020 to allow processing circuitry 1020 toprocess the input information. For example, input interfaces, devices,and circuits may include a microphone, a proximity or other sensor,keys/buttons, a touch display, one or more cameras, a USB port, or otherinput elements. Output interfaces, devices, and circuits are configuredto allow output of information from wireless device 1000, and areconnected to processing circuitry 1020 to allow processing circuitry1020 to output information from wireless device 1000. For example,output interfaces, devices, or circuits may include a speaker, adisplay, vibrating circuitry, a USB port, a headphone interface, orother output elements. Using one or more input and output interfaces,devices, and circuits, wireless device 1000 may communicate with endusers and/or the wireless network, and allow them to benefit from thefunctionality described herein.

As another example, wireless device 1000 may include power supplycircuitry 1030. The power supply circuitry 1030 may comprise powermanagement circuitry. The power supply circuitry may receive power froma power source, which may either be comprised in, or be external to,power supply circuitry 1030. For example, wireless device 1000 maycomprise a power source in the form of a battery or battery pack whichis connected to, or integrated in, power supply circuitry 1030. Othertypes of power sources, such as photovoltaic devices, may also be used.As a further example, wireless device 1000 may be connectable to anexternal power source (such as an electricity outlet) via an inputcircuitry or interface such as an electrical cable, whereby the externalpower source supplies power to power supply circuitry 1030.

Power supply circuitry 1030 may be connected to radio front-endcircuitry 1010, processing circuitry 1020, and/or computer-readablestorage medium 1025 and be configured to supply wireless device 1000,including processing circuitry 1020, with power for performing thefunctionality described herein.

Wireless device 1000 may also include multiple sets of processingcircuitry 1020, computer-readable storage medium 1025, radio circuitry1010, and/or antenna 1005 for different wireless technologies integratedinto wireless device 1000, such as, for example, GSM, WCDMA, LTE, NR,WiFi, or Bluetooth wireless technologies. These wireless technologiesmay be integrated info the same or different chipsets and othercomponents within wireless device 1000.

Wireless device 1000, in various embodiments, is adapted to carry outany of a variety of combinations of the features and techniquesdescribed herein. In some embodiments, for example, processing circuitry1020, e.g., using antenna 1005 and radio front-end circuitry 1010, isconfigured to receive a downlink signal comprising an uplink accessconfiguration index, use the uplink access configuration index toidentify an uplink access configuration from among a predeterminedplurality of uplink access configurations, and transmit to the wirelesscommunications network according to the identified uplink accessconfiguration. As discussed in Section 3.22 above, this uplink accessconfiguration index is a pointer into a table of uplink accessconfigurations. This pointer may be retrieved, for example, from an SSI,as described above, while the uplink access configurations are receivedas an AIT. As discussed in detail above, an advantage arising from theuse of an uplink access configuration index is that broadcastedinformation can be reduced. The plurality of uplink accessconfigurations from which a particular uplink access configuration isretrieved, using, the uplink access configuration index, can bedistributed separately from the broadcasting of the index itself.

Processing circuitry 1020 is also configured to receive, in a firstsubframe, a first OFDM transmission formatted according to a firstnumerology and receiving, in a second subframe, a second OFDMtransmission formatted according to a second numerology, the secondnumerology differing from the first numerology. Note that a“numerology,” as that term is used herein, refers to a particularcombination of OFDM subcarrier bandwidth, cyclic prefix length, andsubframe length. The term subcarrier bandwidth, which refers to thebandwidth occupied by a single subcarrier, is directly related to, andis sometimes used interchangeably, with subcarrier spacing. As discussedin detail above, e.g., in Section 2.3, the availability and use ofdifferent numerologies allows for better matching of the physical layerto specific applications and use case requirements.

In some embodiments, the components of wireless device 1000, and inparticular processing circuitry 1020, are also configured to perform amethod 18200 as illustrated in FIG. 182. The method 18200 includesreceiving a downlink signal comprising an uplink access configurationindex, using the uplink access configuration index to identify an uplinkaccess configuration from among a predetermined plurality of uplinkaccess configurations, and transmitting to the wireless communicationsnetwork according to the identified uplink access configuration (block18210). The method 18200 also includes receiving, in a first subframe, afirst OFDM transmission formatted according to a first numerology andreceiving, in a second subframe, a second OFDM transmission formattedaccording to a second numerology, the second numerology differing fromthe first numerology (block 18220). The first OFDM transmission may havea numerology according to the specifications for LTE.

As an example, the first and second numerologies may comprise subframesof first and second subframe lengths, respectively, where the firstsubframe length differs from the second subframe length. The firstnumerology may also have a first subcarrier spacing (or first subcarrierbandwidth) and the second numerology may have a second subcarrierspacing (or second subcarrier bandwidth), where the first subcarrierspacing differs from the second subcarrier spacing.

In some embodiments, the method 18200 discussed above or another methodmay further include receiving and processing first Layer 2 data on afirst physical data channel and receiving and processing second Layer 2data on a second physical data channel, as shown at blocks 18230 and18232 of FIG. 183. Examples of these were provided above, where thesefirst and second physical data channels were referred to asretransmittable and direct channels. or rPDCH and dPDCH, respectively.The receiving and processing of the first Layer 2 data comprises the useof soft HARQ combining, and the receiving and processing of the secondLayer 2 data comprises no soft HARQ combining. This may include using acommon set of demodulation reference signals for receiving both thefirst and second Layer 2 data. An advantage of this use of two types ofphysical data channels is that the error correction and overheadassociated with each of the channels can be better matched to thespecific types of data carried by the respective channels.

In some cases, a single Radio Resource Control (RRC) approach may beused for handling both the first and second OFDM transmissions, e.g., incombination with some or all of the features discussed above. Thissingle-RRC approach was discussed above, for example, in Section 2.1.4.Note that in the detailed discussion above, the term “RRC” is frequentlyused as a shorthand for the more precise term Radio Resource Controlprotocol layer, or RRC protocol layer, which is the collection ofprocedures that provides Radio Resource Control, e.g., as specified byindustry standards and as typically implemented with correspondingsoftware modules in wireless devices and radio network equipment. Forexample, the method 18200 or another method, as shown in FIG. 184, mayfurther include processing data from the first OFDM transmission using afirst MAC protocol layer (block 18240) and processing data from thesecond OFDM transmission using a second MAC protocol layer, where thefirst MAC protocol layer differs from the second MAC protocol layer(block 18242). This method may further include processing messagesreceived from each of the first and second MAC protocol layers using asingle, common RRC protocol layer (block 18244). An advantage of thisapproach is that the RRC handling for the two physical channels, whichmay be an LTE-based and an NX-based channel, for example, is that theRRC handling is more tightly integrated and efficient.

In some cases, a dual-RRC approach may be used instead, again asdiscussed in Section 2.1.4, for example. In this case, the method 18200or another method, as shown in FIG. 185, further includes processingdata from the first OFDM transmission using a first MAC protocol layer(block 18250) and processing data from the second OFDM transmissionusing a second MAC protocol layer, where the first MAC protocol layerdiffers from the second MAC protocol layer (block 18252). The method18200 may further include processing messages received via the first MACprotocol layer using a first RRC protocol layer and processing messagesreceived via the second MAC protocol layer using a second RRC protocollayer, where the first RRC protocol layer differs from the second RRCprotocol layer (block 18256). At least a first one of the first andsecond RRC protocol layers is configured to pass selected RRC messagesto the other one of the first and second RRC protocol layers. Theselected RRC messages are RRC messages received and processed by thefirst one of the first and second RRC protocol layers but targeted forthe other one of the first and second RRC protocol layers. As wasdiscussed in Section 2.1.4.2, this approach provides for independentspecification of the RRC protocol layers in the context of operatingwith two different RATs (such as NX and LTE), and allows each RRCprotocol layer to be modified independently of the other.

The method 18200 or another method, as shown in FIG. 186, may furtherinclude transmitting third Layer 2 data on a third physical data channel(block 18260) and transmitting fourth Layer 2 data on a fourth physicaldata channel (block 18262). The transmitting of the third Layer 2 datacomprises the use of a HARQ process supporting soft combining, and thetransmitting of the fourth Layer 2 data comprises no HARQ process. Thesethird and fourth physical data channels correspond to theretransmittable and direct channels discussed in detail above.

In some cases, the method 18200 or another method, as shown in FIG. 187,includes operating in a connected mode for one or more first intervalsand operating in a dormant mode for one or more second intervals, wherethe first and second OFDM transmissions are performed in the connectedmode (block 18270). Details of such a dormant state in the NX contextwere provided above, e.g., in Section 1.2. Operating in the dormant modecomprises monitoring signals carrying tracking area identifiers (block18272), comparing tracking area identifiers received during themonitoring with a tracking area identifier list (block 18274), andnotifying the wireless communication network in response to determiningthat a received tracking area identifier is not on the list butotherwise refraining from notifying the wireless communication networkin response to receiving changing tracking area identifiers (block18276). Example details of this tracking-related behavior are describedabove, in Section 3.2.4.1. In the detailed discussion above, examples ofthese tracking area identifiers were referred to as Tracking RAN AreaCodes (TRAC), which correspond to a particular Tracking RAN Area andwhich may be received in a Tracking RAN Area Signal Index. Note thatthis dormant state allows the wireless device to move around within atracking area without reporting to the network, thus providing for moreefficient operation and less signaling.

The method 18200 may include transmitting, to the wirelesscommunications network, a capability pointer, the capability pointeridentifying a set of capabilities, for the wireless device, stored inthe wireless communications network. Details of this approach areprovided above, in Section 2.1.5.3. As noted there, this approach allowsfor a continuing evolution of new wireless device capabilities, withoutrequiring constant updates of the signaling to indicate thosecapabilities.

As discussed in extensive detail above, wireless devices according tomany of the embodiments described herein may use scheduledtransmissions, contention-based transmissions, or a combination of both.Thus, the method 18200 may include transmitting to the wirelesscommunications network using a contention-based access protocol. Thecontention-based access protocol may comprise a listen-before-talk (LBT)access mechanism.

The method 18200 or another method, as shown in FIG. 188, may includemeasuring a first mobility reference signal on a first received beam(block 18280) and measuring a second mobility reference signal on asecond received beam, where the second mobility reference signal differsfrom the first mobility reference signal (block 18282). These mobilityreference signals are referred to as MRS in the detailed systemdescribed above, e.g., in the discussions of beam-based transmission andfeedback in Section 3.4, and in the discussion of mobility in Section3.5. The method 18200 may further include reporting results of measuringthe first and second mobility reference signals to the wirelesscommunications network (block 18284). The method 18200 may also includereceiving, in response to reporting the results, a command to switchfrom receiving data on a current downlink beam to receiving data on adifferent downlink beam (block 18286). The method 18200 may includereceiving a timing advance value for application to the differentdownlink beam (block 18288). This approach provides for a beam-basedactive mobility, detailed in sections 3.5.2 to 3.5.4. as distinct fromthe cell-based mobility used in conventional wireless systems.

5.2 Radio Network Equipment and Methods

As used herein, the term “network equipment” refers to equipmentcapable, configured, arranged and/or operable to communicate directly orindirectly with a wireless device and/or with other equipment in thewireless communication network that enable and/or provide wirelessaccess to the wireless device. Examples of network equipment include,but are not limited to, access points (APs), in particular radio accesspoints. Network equipment may represent base stations (BSs), such asradio base stations. Particular examples of radio base stations includeNode Bs, and evolved Node Bs (eNBs). Base stations may be categorizedbased on the amount of coverage they provide (or, stated differently,their transmit power levels) and may then also be referred to as femtobase stations, pico base stations, micro base stations, or macro basestations. “Network equipment” also includes one or more (or all) partsof a distributed radio base station such as centralized digital unitsand/or remote radio units (RRUs), sometimes referred to as Remote RadioHeads (RRHs). Such remote radio units may or may not be integrated withan antenna as an antenna integrated radio. Parts of a distributed radiobase stations may also be referred to as nodes in a distributed antennasystem (DAS).

As a particular non-limiting example, a base station may be a relay nodeor a relay donor node controlling a relay.

Yet further examples of network equipment include multi-standard radio(MSR) radio equipment such as MSR BSs, network controllers such as radionetwork controllers (RNCs) or base station controllers (BSCs), basetransceiver stations (BTSs), transmission points, transmission nodes.Multi-cell/multicast Coordination Entities (MCEs), core network nodes(e.g., MSCs, MMEs), O&M nodes, OSS nodes, SON nodes, positioning nodes(e.g., E-SMLCs), and/or MDTs. More generally, however, network equipmentmay represent any suitable device (or group of devices) capable,configured, arranged, and/or operable to enable and/or provide awireless device access to the wireless communication network or toprovide some service to a wireless device that has accessed the wirelesscommunication network.

As used herein, the term “radio network equipment” is used to refer tonetwork equipment that includes radio capabilities. Thus, examples ofradio network equipment are the radio base stations and radio accesspoints discussed above. It will be appreciated that some radio networkequipment may comprise equipment that is distributed—such as thedistributed radio base stations (with RRHs and/or RRUs) discussed above.It will be appreciated that the various references herein to eNBs,eNodeBs, Node Bs, and the like are referring to examples of radionetwork equipment. It should also be understood that the term “radionetwork equipment” as used herein may refer to a single base station ora single radio node, in some cases, or to multiple base stations ornodes, e.g., at different locations. In some cases, this document mayrefer to an “instance” of radio network equipment, to more clearlydescribe certain scenarios where multiple distinct embodiments orinstallations of radio equipment are involved. However, the lack ofreference to an “instance” in connection with a discussion of radionetwork equipment should not be understood to mean that only a singleinstance is being referred to. A given instance of radio networkequipment may alternatively be referred to as a “radio network node,”where the use of the word “node” denotes that the equipment referred tooperate as a logical node in a network, but does not imply that allcomponents are necessarily co-located.

While radio network equipment may include any suitable combination ofhardware and/or software, an example, of an instance of radio networkequipment 1100 is illustrated in greater detail by FIG. 189. As shown inFIG. 189, example radio network equipment 1100 includes an antenna 1105,radio front-end circuitry 1110, and processing circuitry 1120, which inthe illustrated example includes a computer-readable storage medium1025, one or more memory devices. Antenna 1105 may include one or moreantennas or antenna arrays, and is configured to send and/or receivewireless signals, and is connected to radio front-end circuitry 1110. Incertain alternative embodiments, radio network equipment 1100 may notinclude antenna 1005, and antenna 1005 may instead be separate fromradio network equipment 1100 and be connectable to radio networkequipment 1100 through an interface or port. In some embodiments, all orparts of radio front-end circuitry 1110 may be located at one or severallocations apart from the processing circuitry 1120, e.g., in a RRH orRRU. Likewise, portions of processing circuitry 1120 may be physicallyseparated from one another. Radio network equipment 1100 may alsoinclude communication interface circuitry 1140 for communicating withother network nodes, e.g., with other radio network equipment and withnodes in a core network.

Radio front-end circuitry 1110, which may comprise various filters andamplifiers, for example, is connected to antenna 1105 and processingcircuitry 1120 and is configured to condition signals communicatedbetween antenna 1105 and processing circuitry 1120. In certainalternative embodiments, radio network equipment 1100 may not includeradio front-end circuitry 1110, and processing circuitry 1120 mayinstead be connected to antenna 1105 without radio front-end circuitry1110. In some embodiments, radio-frequency circuitry 1110 is configuredto handle signals in multiple frequency bands, in some casessimultaneously.

Processing circuitry 1120 may include one or more of RF transceivercircuitry 1121, baseband processing circuitry 1122, and applicationprocessing circuitry 1123. In some embodiments, the RF transceivercircuitry 1121, baseband processing circuitry 1122, and applicationprocessing circuitry 1123 may be on separate chipsets. In alternativeembodiments, part or all of the baseband processing circuitry 1122 andapplication processing circuitry 1123 may be combined into one chipset,and the RF transceiver circuitry 1121 may be on a separate chipset. Instill alternative embodiments, part or all of the RF transceivercircuitry 1121 and baseband processing circuitry 1122 may be on the samechipset, and the application processing circuitry 1123 may be on aseparate chipset. In yet other alternative embodiments, part or all ofthe RF transceiver circuitry 1121, baseband processing circuitry 1122,and application processing circuitry 1123 may be combined in the samechipset. Processing circuitry 1120 may include, for example, one or morecentral CPUs, one or more microprocessors, one or more ASICs, and/or oneor more field FPGAs.

In particular embodiments, some or all of the functionality describedherein as being relevant to radio network equipment, radio basestations, eNBs, etc., may be embodied in radio network equipment or, asan alternative may be embodied by the processing circuitry 1120executing instructions stored on a computer-readable storage medium1125, as shown in FIG. 183. In alternative embodiments, some or all ofthe functionality may be provided by the processing circuitry 1120without executing instructions stored on a computer-readable medium,such as in a hard-wired manner. In any of those particular embodiments,whether executing instructions stored on a computer-readable storagemedium or not, the processing circuitry can be said to be configured toperform the described functionality. The benefits provided by suchfunctionality are not limited to the processing circuitry 1120 alone orto other components of the radio network equipment, but are enjoyed bythe radio network equipment 1100 as a whole, and/or by end users and thewireless network generally.

The processing circuitry 1120 may be configured to perform anydetermining operations described herein. Determining as performed byprocessing circuitry 1120 may include processing information obtained bythe processing circuitry 1120 by, for example, converting the obtainedinformation into other information, comparing the obtained informationor converted information to information stored in the radio networkequipment, and/or performing one or more operations based on theobtained information or converted information, and as a result of saidprocessing making a determination.

Antenna 1105, radio front-end circuitry 1110, and/or processingcircuitry 1120 may be configured to perform any transmitting operationsdescribed herein. Any information, data and/or signals may betransmitted to any network equipment and/or a wireless device. Likewise,antenna 1105, radio front-end circuitry 1110, and/or processingcircuitry 1120 may be configured to perform any receiving operationsdescribed herein as being performed by a radio network equipment. Anyinformation, data and/or signals may be received from any networkequipment and/or a wireless device.

Computer-readable storage medium 1125 is generally operable to storeinstructions, such as a computer program, software, an applicationincluding one or more of logic, rules, code, tables, etc. and/or otherinstructions capable of being executed by a processor. Examples ofcomputer-readable storage medium 1125 include computer memory (forexample, RAM or ROM), mass storage media (for example, a hard disk),removable storage media (for example, a CD or a DVD), and/or any othervolatile or non-volatile, non-transitory computer-readable and/orcomputer-executable memory devices that store information, data, and/orinstructions that may be used by processing circuitry 1120. In someembodiments, processing circuitry 1120 and computer-readable storagemedium 1125 may be considered to be integrated.

Alternative embodiments of the radio network equipment 1100 may includeadditional components beyond those shown in FIG. 189 that may beresponsible for providing certain aspects of the radio networkequipment's functionality, including any of the functionality describedherein and/or any functionality necessary to support the solutiondescribed above. As just one example, radio network equipment 1100 mayinclude input interfaces, devices and circuits, and output interfaces,devices and circuits. Input interfaces, devices, and circuits areconfigured to allow input of information into radio network equipment1100, and are connected to processing circuitry 1120 to allow processingcircuitry 1120 to process the input information. For example, inputinterfaces, devices, and circuits may include a microphone, a proximityor other sensor, keys/buttons, a touch display, one or more cameras, aUSB port, or other input elements. Output interfaces, devices, andcircuits are configured to allow output of information from radionetwork equipment 1100, and are connected to processing circuitry 1120to allow processing circuitry 1120 to output information from radionetwork equipment 1100. For example, output interfaces, devices, orcircuits may include a speaker, a display, a USB port, a headphoneinterface, or other output elements. Using one or more input and outputinterfaces, devices, and circuits, radio network equipment 1100 maycommunicate with end users and/or the wireless network, and allow themto benefit from the functionality described herein.

As another example, radio network equipment 1100 may include powersupply circuitry 1130. The power supply circuitry 1130 may comprisepower management circuitry. The power supply circuitry 1130 may receivepower from a power source, which may either be comprised in, or beexternal to, power supply circuitry 1130. For example, radio networkequipment 1100 may comprise a power source in the form of a battery orbattery pack which is connected to, or integrated in, power supplycircuitry 1130. Other types of power sources, such as photovoltaicdevices, may also be used. As a further example, radio network equipment1100 may be connectable to an external power source (such as anelectricity outlet) via an input circuitry or interface such as anelectrical cable, whereby the external power source supplies power topower supply circuitry 1130.

Power supply circuitry 1130 may be connected to radio front-endcircuitry 1110, processing circuitry 1120, and/or computer-readablestorage medium 1125 and be configured to supply radio network equipment1100, including processing circuitry 1120, with power for performing thefunctionality described herein.

Radio network equipment 1100 may also include multiple sets ofprocessing circuitry 1120, computer-readable storage medium 1125, radiocircuitry 1110, antenna 1105 and/or communication interface circuitry1140 for different wireless technologies integrated into radio networkequipment 1100, such as, for example, GSM, WCDMA, LTE, NR, WiFi, orBluetooth wireless technologies. These wireless technologies may beintegrated into the same or different chipsets and other componentswithin radio network equipment 1100.

One or more instances of the radio network equipment 1100 may be adaptedto carry out some or all of the techniques described herein, in any ofvarious combinations. It will be appreciated that in a given networkimplementation, multiple instances of radio network equipment 1100 willbe in use. In some cases, several instances of radio network equipment1100 at a time may be communicating with or transmitting signals to agiven wireless device or group of wireless devices. Thus, it should beunderstood that while many of the techniques described herein may becarried out by a single instance of radio network equipment 1100, thesetechniques may be understood as carried out by a system of one or moreinstances of radio network equipment 1100, in some cases in acoordinated fashion. The radio network equipment 1100 shown in FIG. 189is thus the simplest example of this system.

In some embodiments, for example, a system of one or more instances ofradio network equipment 1100, and in particular the processing circuitry1120 in such radio network equipment 1100, e.g., using an antenna 1105and radio front-end circuitry 1110, is configured to transmit a firstdownlink signal comprising an uplink access configuration index, theuplink access configuration index identifying an uplink accessconfiguration from among a plurality of predetermined uplink accessconfigurations, and subsequently receive a transmission from a firstwireless device according to the identified uplink access configuration.Note that this transmitting of the uplink access configuration index maybe a broadcast transmission, in that it is not necessarily targeted toany particular wireless device or group of wireless devices. It will beappreciated that these techniques complement the wireless device-basedtechniques described in Section 5.1, and provide the same advantages.The processing circuitry 1120 is also configured to transmit, in a firstsubframe, a first OFDM transmission formatted according to a firstnumerology and transmit, in a second subframe, a second OFDMtransmission formatted according to a second numerology, the secondnumerology differing from the first numerology. Here, each of thesefirst and second OFDM transmissions is typically (but not necessarily)targeted to a particular wireless device or group of wireless devices;the two transmissions here may be targeted to the same wireless deviceor to two different wireless devices. Again, these techniques complementthose described in Section 5.1.

In some embodiments, a system comprising one or more instances of radionetwork equipment 1100 is configured to perform a method 19000, asillustrated in FIG. 190. The method 19000 includes transmitting a firstdownlink signal comprising an uplink access configuration index, theuplink access configuration index identifying an uplink accessconfiguration from among a plurality of predetermined uplink accessconfigurations, and subsequently receiving a transmission from a firstwireless device according to the identified uplink access configuration(block 19010). The method 19000 also includes transmitting, in a firstsubframe, a first OFDM transmission formatted according to a firstnumerology and transmitting, in a second subframe, a second OFDMtransmission formatted according to a second numerology, the secondnumerology differing from the first numerology (block 19020).

In some cases, transmitting the first downlink signal is performed by afirst instance of radio network equipment, while the transmitting of thefirst and second OFDM transmissions is performed by a second instance ofradio network equipment. The first OFDM transmission may have anumerology according to the specifications for LTE.

The first and second numerologies may comprise subframes of first andsecond subframe lengths, respectively, where the first subframe lengthdiffers from the second subframe length. The first numerology may have afirst subcarrier spacing and the second numerology may have a secondsubcarrier spacing, where the first subcarrier spacing differs from thesecond subcarrier spacing.

The method 19000, as further shown in FIG. 190, may include transmittinga second downlink signal comprising an access information signal, theaccess information signal indicating a plurality of uplink accessconfigurations, where the uplink access configuration index identifiesone of the plurality of uplink access configurations (block 19030). Thetransmitting of the second downlink signal may be performed by a thirdinstance of radio network equipment.

In some cases, the method 19000 or another method, as shown in FIG. 191,includes processing and transmitting first Layer 2 data on a firstphysical data channel (block 19040) and processing and transmittingsecond Layer 2 data on a second physical data channel (block 19042). Theprocessing and transmitting of the first Layer 2 data comprises the useof a HARD process supporting soft combining, and the processing andtransmitting of the second Layer 2 data comprises no HARQ process. Thetransmitting of the first and second Layer 2 data may be performed usinga common antenna port, where the method 19000 further includestransmitting a common set of demodulation references, using the commonantenna port, for use in receiving both the first and second Layer 2.Again, these techniques, and the corresponding techniques for receivingphysical data channels discussed immediately below, complement thetechniques discussed in Section 5.1, and provide the same advantages.

The method 19000, as shown in FIG. 192, may include receiving andprocessing third Layer 2 data on a third physical data channel (block19050) and receiving and processing fourth Layer 2 data on a fourthphysical data channel (block 19052), where the receiving and processingof the third Layer 2 data comprises the use of soft HARQ combining andthe receiving and processing of the fourth Layer 2 data comprises nosoft HARQ combining/

In some cases, the transmitting of the first and second OFDMtransmissions may be performed by a single instance of radio networkequipment, in which case the method 19000 or another method, as shown inFIG. 193, may further include processing data for the first OFDMtransmission using a first MAC protocol layer (block 19060) andprocessing data for the second OFDM transmission using a second MACprotocol layer, where the first MAC protocol layer differs from thesecond MAC protocol layer (block 19062). The method 19000 may furtherinclude processing messages to be transported by each of the first andsecond MAC protocol layers, using a single, common RRC protocol layer(block 19064).

In other cases, the transmitting of the first and second OFDMtransmissions is performed by a single instance of radio networkequipment, in which case the method 19000 or another method, as shown inFIG. 194, may further include processing data for the first OFDMtransmission using a first MAC protocol layer (block 19070) andprocessing data for the second OFDM transmission using a second MACprotocol layer, where the first MAC protocol layer differs from thesecond MAC protocol layer (block 19072). The method 19000 furtherincludes processing messages to be transported by the first MAC protocollayer, using a first RRC protocol layer (block 19074), and processingmessages to be transported by the second MAC protocol layer, using asecond RRC protocol layer, where the first RRC protocol layer differsfrom the second RRC protocol layer (block 19076). At least a first oneof the first and second RRC protocol layers is configured to passselected RRC messages to the other one of the first and second RRCprotocol layers, the selected RRC messages being RRC messages receivedand processed by the first one of the first and second RRC protocollayers but targeted for the other one of the first and second RRCprotocol layers.

The method 19000 or another method, as shown in FIG. 195, may includereceiving, from a second wireless device, a capability pointer, thecapability pointer identifying a set of capabilities for the secondwireless device (block 19080), and retrieving the set of capabilitiesfor the second wireless device, from a database of stored capabilitiesfor a plurality of wireless devices, using the received capabilitypointer (block 19082).

The method 19000 may include transmitting to a third wireless device,using a contention-based protocol. The contention-based access protocolmay comprise an LBT access mechanism.

In some embodiments, the method 19000 or another method, as shown inFIG. 196, includes receiving a random access request message from afourth wireless device, via an uplink beam formed using multipleantennas at one of the one or more instances of radio network equipment(block 19090), estimating an angle-of-arrival corresponding to therandom access request message (block 19092) and transmitting a randomaccess response message, using a downlink beam formed using multipleantennas at the one of the one or more instances of the radio networkequipment (block 19094). Forming the downlink beam is based on theestimated angle-of-arrival. The uplink beam may be a swept uplink beam.A width of the downlink beam may be based on an estimated quality of theestimated angle-of-arrival. Note that exemplary details of a randomaccess procedure in NX are described in Section 3.2.52, whilemulti-antenna aspects of the random access procedure are provided inSection 3.4.5.2.

The method 19000 or another method, as shown in FIG. 197, may includeserving a fifth wireless device, where serving the fifth wireless devicecomprises sending data from the fifth wireless device to a first networknode or first set of network nodes, according to a first network sliceidentifier associated with the fifth wireless device (block 19096). Themethod 19000 may also include serving a sixth wireless device, whereserving the sixth wireless device comprises sending data from the sixthwireless device to a second network node or second set of network nodes,according to a second network slice identifier associated with the sixthwireless device (block 19098). The second network slice identifierdiffers from the first network slice identifier, and the second networknode or second set of network nodes differs from the first network nodeor first set of network nodes.

5.3 Functional Representations and Computer Program Products

FIG. 198 illustrates an example functional module or circuitarchitecture as may be implemented in a wireless device 1000, e.g.,based on the processing circuitry 1020. The illustrated embodiment atleast functionally includes an access configuration module 19802 forreceiving a downlink signal comprising an uplink access configurationindex, using the uplink access configuration index to identify an uplinkaccess configuration from among a predetermined plurality of uplinkaccess configurations, and transmitting to the wireless communicationsnetwork according to the identified uplink access configuration. Theimplementation also includes a receiving module 19804 for receiving, ina first subframe, a first OFDM transmission formatted according to afirst numerology and receiving, in a second subframe, a second OFDMtransmission formatted according to a second numerology, the secondnumerology differing from the first numerology.

In some embodiments, the implementation includes a receiving andprocessing module 19806 for comprising receiving and processing firstLayer 2 data on a first physical data channel and receiving andprocessing second Layer 2 data on a second physical data channel,wherein the receiving and processing of the first Layer 2 data comprisesthe use of soft HARQ combining and wherein the receiving and processingof the second Layer 2 data comprises no soft HARQ combining.

In some embodiments, the implementation includes a transmitting module19808 for transmitting, to the wireless communications network, acapability pointer, the capability pointer identifying a set ofcapabilities, for the wireless device, stored in the wirelesscommunications network.

In some embodiments, the implementation includes a measuring module19810 for measuring a first mobility reference signal on a firstreceived beam and for measuring a second mobility reference signal on asecond received beam, the second mobility reference signal differingfrom the first mobility reference signal. This implementation alsoincludes a reporting module 19812 for reporting results of measuring thefirst and second mobility reference signals to the wirelesscommunications network.

FIG. 199 illustrates an example functional module or circuitarchitecture as may be implemented in the radio network equipment 1100,e.g., based on the processing circuitry 1120. The illustrated embodimentat least functionally includes an access configuration module 19902 fortransmitting a first downlink signal comprising an uplink accessconfiguration index, the uplink access configuration index identifyingan uplink access configuration from among a plurality of predetermineduplink access configurations, and subsequently receiving a transmissionfrom a first wireless device according to the identified uplink accessconfiguration. The implementation also includes a transmitting module19904 or transmitting, in a first subframe, a first OFDM transmissionformatted according to a first numerology and transmitting, in a secondsubframe, a second OFDM transmission formatted according to a secondnumerology, the second numerology differing from the first numerology.

In some embodiments, the implementation includes a transmitting module19906 for transmitting a second downlink signal comprising an accessinformation signal, the access information signal indicating a pluralityof uplink access configurations, wherein the uplink access configurationindex identifies one of the plurality of uplink access configurations.

In some embodiments, the implementation includes a processing andtransmitting module 19908 for processing and transmitting first Layer 2data on a first physical data channel and processing and transmittingsecond Layer 2 data on a second physical data channel wherein theprocessing and transmitting of the first Layer 2 data comprises the useof a HARQ process supporting soft combining and wherein the processingand transmitting of the second Layer 2 data comprises no HARQ process.

In some embodiments, the implementation includes a receiving module19910 for receiving, from a second wireless device, a capabilitypointer, the capability pointer identifying a set of capabilities forthe second wireless device. This implementation also includes aretrieving module 19912 for retrieving the set of capabilities for thesecond wireless device, from a database of stored capabilities for aplurality of wireless devices, using the received capability pointer.

In some embodiments, the implementation includes a receiving module19914 for receiving a random access request message from a fourthwireless device, via an uplink beam formed using multiple antennas atthe radio network equipment. This implementation also includes anestimating module 19916 for estimating an angle-of-arrival correspondingto the random access request message and a transmitting module 19918 fortransmitting a random access response message, using a downlink beamformed using multiple antennas at the radio network equipment, whereinforming the downlink beam is based on the estimated angle-of-arrival.

Appendix: Abbreviations

Abbreviation Explanation 2G 2nd Generation 3G 3rd Generation 3GPP 3rdGeneration Partnership Project 4G 4th Generation 5G 5th Generation 5GPPP5G Infrastructure Public-Private Partnership 5GTB 5th Generation TestbedABR Automatic Base station Relation ACK Acknowledgement ADSS AlignedDirectional Sounding and Sensing AGC Automatic Gain Control AGVAutomated Guided Vehicle AIT Access Information Table AMM Active ModeMobility AN Access Node ANR Automatic Neighbor Relations AP Access PointARQ Automatic Repeat reQuest AS Access Stratum ASA Authorized SharedAccess AVR Automatic Virtual beam Relations BB Baseband BBF BasebandFunction BBU Baseband Unit BER Bit Error Rate BF Beamforming BH BackhaulBIO Beam Individual Offset BLEP Block Error Probability BLER Block ErrorRate BRS Beam Reference Signal BS Base Station BS2BS Base Station toBase Station BSID Base Station Identifier BW Band Width CA CarrierAggregation CAPEX Capital Expenditures CB Contention-based CCE ControlChannel Element CCP Cluster Coordinating Point CDMA2000 Cellular systemspecified by 3GPP2 CEPT Conférence européenne des administrations despostes et télécommunications CF Compute-and-Forward CH Cluster Head CIOCell Individual Offset CMAS Commercial Mobile Alert System C-MTCCritical Machine Type Communication CN Core Network COMP CoordinatedMulti-Point CP Cyclic Prefix CPRI Common Public Radio Interface CQIChannel Quality Information CRC Cyclic Redundancy Check CRSCell-specific Reference Signal CSI Channel State Information CTS Clearto Send D2D Device-to-Device DAC Digital-to-Analog Converter DC DualConnectivity DCI Downlink Control Information DDOS Distributed Denial ofService DFT Discrete Fourier Transform DFTS Discrete FourierTransform-Spread DL Downlink DLIM Directional Link Interference Map DMRSDemodulation Reference Signal DN Destination Node DRB Dedicated RadioBearer DRX Discontinuous Reception DSSI Directional Sounding and SensingInterval DSSP Directional Sounding and Sensing Period DSSW DirectionalSounding and Sensing Window DTX Discontinuous Transmission E2E End toEnd E3F Energy Efficiency Evaluation Framework EAB Extended Access ClassBarring ECGI E-UTRAN Cell Global Identifier ECM EPS ConnectionManagement EGPRS Enhanced General Packet Radio Service EIRP EquivalentIsotropically Radiated Power eNB Evolved Node B EMBB Enhanced MobileBroadband EMF Electromagnetic Fields EMM EPS Mobility Management(Protocol) EPC Evolved Packet Core EPS Evolved Packet Subsystem ETSIEuropean Telecommunications Standards Institute ETWS Earthquake TsunamiWarning System EVM Error Vector Magnitude FCC Federal CommunicationsCommission FDD Frequency Division Duplex FDMA Frequency DivisionMultiple Access FFT Fast Fourier Transform FPGA Field-Programmable GateArray FPS Frames Per Second FRA Future Radio Access GB Guard band GERANGSM Edge Radio Access Network GFTE Group Function Technology GLDBGeolocation Database GNSS Global Navigation Satellite Systems GPRSGeneral Packet Radio Service GPS Global Positioning System GSM GlobalSystem for Mobile communications (Groupe Speciale Mobile) GW GatewayHARQ Hybrid ARQ HO Handover HW Hardware I2D Infrastructure-To-Device IDIdentity IE Information Element IFFT Inverse Fast Fourier Transform IIDIndependent Identically Distributed IM Interference Measurement IMRInterference Measurement Resource IMSI International Mobile SubscriberIdentify IMT International Mobile Telecommunications IMT2020International Mobile Telecommunications 2020 IOT Internet of Things IPInternet Protocol IR Incremental Redundancy IRAT Inter RAT ISD InterSite Distance ITU International Telecommunication Union IUA InstantUplink Access KPI Key Performance Indicator L1 Layer 1 L2 Layer 2 L3Layer 3 LAA License Assisted Access LAT Listen-after-talk LBTListen-before-talk LCID Logical Channel ID LDPC Low Density Parity CheckLO Local Oscillator LOS Line of sight LSA License Shared Access LTE LongTerm Evolution MAC Medium Access Control MBB Mobile Broadband MBMSMultimedia Broadcast Multicast Services MBSFN Multicast-broadcastsingle-frequency network MCS Modulation and Coding Scheme METIS Mobileand Wireless Communications Enablers for the 2020 Information SocietyMIB Master Information Block MIMO Multiple Input Multiple Output MMEMobility Management Entity MMSE Minimum Mean Square Error MMW MillimeterWave MPD Multi-Point Diversity MRS Mobility and Access Reference SignalMRT Maximum Ratio Transmission MTC Machine Type Communication MU MultiUser NA Not Applicable NACK Negative Acknowledgement NAK NegativeAcknowledgement NAS Non-Access Stratum NB Narrow Band NDI New DataIndicator NFV Network Function Virtualization NGMN Next GenerationMobile Networks NLOS Non-Line-of-Sight NNTS Notify-Not-To-Send NTSNotify-To-Send NR New Radio NW Network NX The term NX is not anabbreviation, and is to be interpreted as a construct that denotes the“Next” generation, as well as a multiplier of capabilities OAMOperation-and-Maintenance OCC Orthogonal Cover Code OFDM OrthogonalFrequency Division Multiplex OOS Out Of Synch OPEX OperationalExpenditures OSS Operation and Support System OTT Over The Top PA PowerAmplifier PACH Physical Anchor Channel PAPR Peak to Average Power RatioPBCH Physical Broadcast Channel PCCH Paging Control Channel PDCCHPhysical Downlink Control Channel PDCH Physical Data Channel PDCP PacketData Convergence Protocol PDSCH Physical Downlink Shared Channel PDUPacket Data Unit PHR Power Head-room Reporting PHY Physical (layer) PICHPaging Indicator Channel PIT Positioning Information Table PLMN PublicLand Mobile Network PLNC Physical-Layer Network Coding PMCH PagingMessage Channel PME Positioning Management Entity PMI Precoder MatrixIndicator PPF Packet Processing Function PRACH Physical Random AccessChannel PRS Positioning Reference Signal PS Public Safety PSD PowerSpectral Density PSM Power Saving Mode PSS Primary SynchronizationSequence PUCCH Physical Uplink Control Channel PUSCH Physical UplinkShared Channel PWS Public Warning System QAM Quadrature AmplitudeModulation QMF Quantize-Map-and Forward QPSK Quadrature Phase ShiftKeying RA Random Access RACH Random Access Channel RAN Radio AccessNetwork RAR Random Access Response RAS Re-configurable Antenna SystemsRAT Radio Access Technology RB Resource Block RBS Radio Base Station RCFRadio Controller Function RF Radio Frequency RLC Radio Link Control(Protocol) RLF Radio Link Failure RLP Radio Link Problem RN RadioNetwork RNTI Radio Network Temporary Identifier RRC Radio ResourceControl (Protocol) RRM Radio Resource Management RRS ReciprocityReference Signal RS Reference Signal RSI Reception Status Indicator RSRPReference Signal Received Power RTS Request-To-Send RTT Round Trip TimeRU Radio Unit RX Receive S1 Interface between RAN and CN in LTE S1AP S1Application Protocol (signaling protocol) S2 Interface used for Wi-Fiintegration in EPC SA System Architecture SAN Serving Access Node SARSpecific Absorption Rate SC Spatially-Coupled SDN Software DefinedNetworking SeNB Secondary eNB SDU Service Data Unit SFN Single FrequencyNetwork SG Scheduling Grant SI System Information SIB System InformationBlock SIM Subscriber Identity Module SINR Signal to Interference andNoise Ratio SIR Signal to Interference Ratio SLNR Signal to Leakage andNoise Ratio SLSS Side-Link Sync Signal SN Source Node SNR Signal toNoise Ratio SON Self-Organizing Network SR Scheduling Request SRBSignaling Radio Bearer SRS Sounding Reference Signal SRU SoundingResource Unit SS Signature Sequence SSB SSI Block SSI Signature SequenceIndex SSS Secondary Synchronization Sequence SU Single-User SW SoftwareSVD Singular Value Decomposition SWEA An Ericsson StandardizationProgram TA Timing Advance TA Tracking Area TAU Tracking Area Update TBTransport Block TBD To Be Defined TCO Temperature Controlled OscillatorTCP Transmission Control Protocol TDD Time Division Duplex TDOA TimeDifference Of Arrival (positioning method) TEA The EricssonArchitecture? TM Transmission Mode TMSI Temporary Mobile SubscriberIdentity TRA Tracking RAN Area TRAC Tracking RAN Area Code TRAS TrackingRAN Area Signal TRASI Tracking RAN Area Signal Index TRASS Tracking RANArea Signal Synchronization TSS Time and Frequency SynchronizationSignal TTI Transmission Time Interval TV Television TX Transmit UCIUplink Control Information UE User Equipment UE2UE UE to UEcommunication UEID UE Identity UI User Interface UL Uplink ULA UniformLinear Array UP User Plane URA UTRAN Registration Area URL UniformResource Locator? US United States (of America) USIM UniversalSubscriber Identity Module USS Uplink Synchronization Signal UTRA UMTSTerrestrial Radio Access (3G) UTRAN UMTS Terrestrial Radio AccessNetwork (3G RAN) V2V Vehicle to Vehicle V2X Vehicle to Anything VBVirtual Beam WCDMA Wideband Code Division Multiple Access (3G) WINNERWireless world INitiative NEw Radio (EU project) WRC World RadioConference (ITU) X2 Interface between eNBs in LTE X2AP X2 ApplicationProtocol (signaling protocol over X2) XO Crystal Oscillator ZF ZeroForcing

What is claimed is:
 1. A method in a radio network equipment, the methodcomprising: receiving a message from a first user equipment (UE),according to one of a plurality of uplink access configurations, the oneof the plurality of uplink access configurations corresponding to anuplink access configuration index previously transmitted to the firstUE; and transmitting, in response to the message, first and secondOrthogonal Frequency-Division Multiplexing (OFDM) transmissionsformatted according to first and second numerologies, respectively, thesecond numerology differing from the first numerology.
 2. The method ofclaim 1, wherein the first numerology has a first subcarrier spacing andthe second numerology has a second subcarrier spacing, the firstsubcarrier spacing differing from the second subcarrier spacing.
 3. Themethod of claim 1, wherein the method further comprises: broadcastingsystem access information for accessing the wireless communicationsnetwork; and, transmitting additional system information in response toa request from the first UE.
 4. The method of claim 1, wherein themethod further comprises: transmitting first and second mobilityreference signals on first and second beams, respectively; and receivinga report, from a user equipment (UE), the report comprising results ofmeasurements of the first and second mobility reference signals.
 5. Themethod of claim 1, wherein the method further comprises: transmitting,in a first-in-time OFDM symbol, downlink control signaling and dedicateduser data.
 6. The method of claim 1, wherein the method furthercomprises: processing data for said first OFDM transmission using afirst Medium Access Control (MAC) protocol layer and processing data forsaid second OFDM transmission using a second MAC protocol layer, thefirst MAC protocol layer differing from the second MAC protocol layer,and processing messages to be transported by each of said first andsecond MAC protocol layers, using a single, common, Radio ResourceControl (RRC) protocol layer.
 7. A method in a user equipment (UE) foroperating in a wireless communications network, the method comprising:transmitting a message to the wireless communications network accordingto one of plurality of uplink access configurations, the one of theplurality of uplink access configurations corresponding to an uplinkaccess configuration index previously received by the first UE; andreceiving, in response to the transmitted message, first and secondOrthogonal Frequency-Division Multiplexing (OFDM) transmissionsformatted according to first and second numerologies, respectively, thesecond numerology differing from the first numerology.
 8. The method ofclaim 7, wherein the first numerology has a first subcarrier spacing andthe second numerology has a second subcarrier spacing, the firstsubcarrier spacing differing from the second subcarrier spacing.
 9. Themethod of claim 7, wherein the method further comprises: receivingbroadcasted system access information and using the received systemaccess information for accessing the wireless communications network;requesting additional system information from the wirelesscommunications network; and receiving additional system information fromthe wireless communications network, in response to said requesting. 10.The method of claim 7, wherein the method further comprises: processingdata from the first OFDM transmission using a first Medium AccessControl (MAC) protocol layer and processing data from said second OFDMtransmission using a second MAC protocol layer, said first MAC protocollayer differing from said second MAC protocol layer, and wherein themethod further comprises processing messages received from each of saidfirst and second MAC protocol layers using a single, common RadioResource Control (RRC) protocol layer.
 11. The method of claim 7,wherein the method further comprises: measuring first and secondmobility reference signals on first and second received beams,respectively, the second mobility reference signal differing from thefirst mobility reference signal; and reporting results of measuring saidfirst and second mobility reference signals to the wirelesscommunications network.
 12. A radio network equipment comprising radiocircuitry, and processing circuitry operatively connected to the radiocircuitry, wherein the processing circuitry in the radio networkequipment is configured to: receive a message from a first userequipment (UE) according to one of a plurality of uplink accessconfigurations, the one of the plurality of uplink access configurationscorresponding to an uplink access configuration index previouslytransmitted to the first UE; and transmit, in response to the message,first and second Orthogonal Frequency-Division Multiplexing (OFDM)transmissions formatted according to first and second numerologies,respectively, the second numerology differing from the first numerology.13. The radio network equipment of claim 12, wherein said processingcircuitry is further configured to: broadcast system access informationfor accessing the wireless communications network; and transmitadditional system information in response to a request from the UE. 14.The radio network equipment of claim 12, wherein said processingcircuitry is further configured to: transmit, in a first-in-time OFDMsymbol, downlink control signaling and dedicated user data.
 15. Theradio network equipment of claim 12, wherein the processing circuitry isfurther configured to: process data for said first OFDM transmissionusing a first Medium Access Control (MAC) protocol layer and processdata for said second OFDM transmission using a second MAC protocollayer, the first MAC protocol layer differing from the second MACprotocol layer, and to process messages to be transported by each ofsaid first and second MAC protocol layers, using a single, common RadioResource Control (RRC) protocol layer.
 16. A user equipment (UE),comprising radio-frequency circuitry, and processing circuitryoperatively connected to the radio-frequency circuitry, wherein theprocessing circuitry is configured to: transmit a message to thewireless communications network according to one of plurality of uplinkaccess configurations, the one of the plurality of uplink accessconfigurations corresponding to an uplink access configuration indexpreviously received by the first UE; and receive, in response to thetransmitted message, first and second Orthogonal Frequency-DivisionMultiplexing (OFDM) transmissions formatted according to first andsecond numerologies, respectively, the second numerology differing fromthe first numerology.
 17. The UE of claim 16, wherein said processingcircuitry is further configured to: receive broadcasted system accessinformation and use the received system access information for accessingthe wireless communications network; request additional systeminformation from the wireless communications network; and receiveadditional system information from the wireless communications network,in response to said requesting.
 18. The UE of claim 16, wherein saidprocessing circuitry is further configured to: process data from saidfirst OFDM transmission using a first Medium Access Control (MAC)protocol layer and process data from said second OFDM transmission usinga second MAC protocol layer, said first MAC protocol layer differingfrom said second MAC protocol layer, and process messages received fromeach of said first and second MAC protocol layers using a single, commonRadio Resource Control (RRC) protocol layer.
 19. The UE of claim 16,wherein the processing circuitry is further configured to: measure firstand second mobility reference signals on first and second receivedbeams, respectively; and report results of measuring the first andsecond mobility reference signals to the wireless communicationsnetwork.